State Highway 345 or SH 345 is a short spur route from US 77 at San Benito northeast to Rio Hondo in deep south Texas. The route was designated in 1942.

SH 345 begins at a junction with US 77 in San Benito. It heads northeast from this junction as it continues through San Benito to an intersection with US 77 Bus.. The highway continues through San Benito to the northeast to an intersection with FM 3462. Heading towards the northeast, the highway continues to a junction with FM 1561. SH 345 reaches its northern terminus at FM 106.