State Route 668 (SR 668) is a short state highway in Washoe County, Nevada. It runs along a small section of Rock Boulevard in Sparks.

State Route 668 begins at the intersection of South Rock Boulevard and Hymer Avenue in an industrial business section of Sparks. The route heads north from there along Rock Boulevard, passing underneath the Union Pacific railroad tracks and interchanging with Interstate 80 (I-80). SR 668 ends after 0.314 miles (0.505 km), at its intersection with Victorian Avenue (I-80 Business).

The route was created on July 1, 1976, during the renumbering of Nevada's state highways.

The entire route is in Sparks, Washoe County.