Utah State Route 123 (SR-123) is a state highway in the U.S. state of Utah. Spanning 11.4 miles (18.3 km), it connects the cities of Sunnyside and East Carbon with US-6 / US-191 in Carbon County.

State Route 123 begins at Sunnyside Junction on US-6/US-191, about 15 miles southeast of Price. It heads east, passing through East Carbon just before reaching Sunnyside at the base of the Book Cliffs. The route continues through Sunnyside, turning to the northeast and terminating shortly after it enters Whitmore Canyon.

The road from Sunnyside Junction through Sunnyside to Columbia was added to the state highway system in 1931, initially numbered SR-124 but changed to SR-123 in 1933. The route was shortened in 1935 by moving the eastern terminus back into Sunnyside, and splitting off the portion from Sunnyside to Columbia as SR-124.

The entire route is in Carbon County.