Pennsylvania Route 356 (PA 356) is an 32-mile (51 km) long state highway located in Westmoreland, Allegheny, Butler, and Armstrong counties in Pennsylvania. The southern terminus is at PA 66 near Oklahoma. The northern terminus is at US 422 in Butler.

PA 356 begins at an intersection with PA 66 in Washington Township, Westmoreland County, heading north on a two-lane undivided road. The route passes through wooded areas with some farm fields and homes, crossing into Allegheny Township. The road continues northwest, heading into farmland with some residential and commercial development. At this point, PA 356 begins to run to the southwest of PA 56, heading through wooded areas of homes and passing through Weinel Crossroads. The route comes to an intersection with PA 56, with that route heading northwest concurrent with PA 356. The road passes more homes and some businesses before PA 56 splits to the west on Leechburg Road. PA 356 winds northwest through woodland with a few residences, continuing into a mix of farmland and woods with some homes. The road passes through Garvers Ferry and widens into a four-lane divided highway, coming to the Donald R. Lobaugh Bridge over the Allegheny River.

Crossing the river, PA 356 briefly passes through Freeport in Armstrong County before heading through a corner of Harrison Township in Allegheny County as it crosses onto the northwest bank of the Allegheny River and becomes Butler Road. A short distance past the river, the route enters Buffalo Township in Butler County and comes to an interchange with Freeport Road, with a southbound exit and an entrance to both directions of PA 356. Here, PA 356 splits into a one-way pair. The northbound direction of PA 356 heads northeast onto 2nd Street, crossing the Buffalo Creek back into Freeport, Armstrong County. The road intersects the southern terminus of PA 128 and turns west onto Buffalo Street, crossing the Buffalo Creek again and rejoining southbound PA 356. Meanwhile, southbound PA 356 heads south on Butler Road, crossing from Freeport, Armstrong County into Buffalo Township, Butler County and coming to ramps to southbound Freeport Road and to northbound PA 356, providing access to PA 128 from southbound PA 356.

After rejoining, the route heads north on three-lane undivided Butler Road, carrying two northbound lanes and one southbound lane as it heads through wooded areas and crosses back into Buffalo Township in Butler County. The road turns northwest and heads into commercial areas in Schuster Heights, widening into a four-lane divided highway as it comes to an interchange with the PA 28 freeway. Past this interchange, PA 356 becomes South Pike Road and becomes a three-lane road with a center left-turn lane, passing a mix of homes and businesses and running through Nolf Corners and Silverville and narrowing back to two lanes. The route heads into a mix of farmland and woodland with some residential and commercial establishments, coming to a junction with the eastern terminus of PA 228 in Sarverville. Here, the road curves to the north-northwest as North Pike Road and runs through more rural areas with some development and passes through Lernerville, where it runs past Lernerville Speedway. PA 356 heads into Winfield Township and runs through open agricultural areas with some woods and homes. The route enters Jefferson Township and heads northwest through rural areas of residences and businesses, passing through Hannahstown. The road runs through more farmland with some patches of woods and development, becoming Freeport Road.

PA 356 continues through rural areas and heads into Summit Township. The route heads through more areas of farms and woods with housing, heading into increasing residential development and turning west into Butler Township. PA 356 turns north onto Center Avenue and passes farms to the west and homes to the east before entering Butler. The road continues through residential areas, turning to the northwest. The route heads into urban areas of homes and businesses, continuing onto East Wayne Street and coming to a bridge over two Buffalo and Pittsburgh Railroad lines. PA 356 curves west and heads into the commercial downtown of Butler, intersecting PA 8. At this point, the route turns north to join PA 8 on South Main Street, a three-lane road with a center left-turn lane that runs through more of the downtown. The road comes to the one-way pair carrying PA 68, at which point PA 356 turns west to join PA 68 on two-lane West Jefferson Street westbound and two-lane West Cunningham Street eastbound. The one-way pair leaves the downtown and heads into residential areas with some businesses, with both directions of PA 68/PA 356 rejoining and heading northwest on two-lane, two-way West Cunningham Street. The two routes turn west onto New Castle Street and pass more development, crossing into Butler Township and becoming New Castle Road. PA 68/PA 356 continues northwest through wooded areas and commercial development, gaining a center left-turn lane. PA 68 splits from PA 356 by heading west on Evans City Road, and PA 356 passes more businesses. The road passes more shopping centers ad well as the Butler Veterans Affairs Medical Center, widening into a five-lane road with a center left-turn lane. PA 356 turns north onto a four-lane divided highway and ends at a cloverleaf interchange with the US 422 freeway, with the divided highway ending at a dead end just north of the interchange.