Route 135 is a state highway in eastern Massachusetts, running from U.S. Route 20 in Northborough east to Interstate 95 (Route 128) in Dedham. The first 13 miles (21 km) of the Boston Marathon, from Hopkinton to Wellesley, follow Route 135.

Route 135 begins at U.S. Route 20 in Northborough. The route follows a generally southeasterly path, interchanging with Route 9 approximately 1-mile (1.6 km) from its beginning. The route continues into Westborough, where it meets Route 30 at a rotary. Route 135 continues southeast, crossing underneath Interstate 90 (the Mass Pike) and Interstate 495, but interchanging with neither. The route enters Hopkinton, and turns northeast at an intersection with West Main Street (access to I-495 is possible using this road). Not far down the road, Route 135 crosses Route 85, continues into Ashland and then into Framingham. In downtown Framingham, Route 135 crosses Route 126 at a rather notorious intersection with railroad crossings, which often cause backups. Route 135 continues into Natick and crosses Route 27 in the center of town. The road continues into Wellesley, passing by the campus of Wellesley College before entering the town center. Route 135 and Route 16 meet at a 5-way intersection and run concurrently for a short distance. Route 135 splits off Route 16 and once again turns southeast onto Great Plain Avenue. The highway enters Needham, and splits off Great Plain Avenue towards Dedham. Upon entering Dedham, Route 135 meets Interstate 95 (Route 128).

Route 135 officially ends at this interchange, although current signage indicates that the route continues eastward (it actually did up to the 1950s). The road that continues after the interchange (West St./Common St.) passes Northeastern University's Dedham campus and meets Route 109 approximately a half mile to the southeast, near Dedham Center.

Route 135 is known by the following street names.

Northborough

Westborough

Hopkinton

Ashland

Framingham

Natick

Wellesley

Needham

Dedham

Originally, the eastern terminus of Route 135 was in Quincy at the current intersection of Route 3A and Route 53. The route was truncated after completion of the Route 128 freeway in the late 1950s made Route 135's routing redundant.