Massachusetts Route 6A is the state road for two sections formerly known as U.S. Route 6 (US 6) on Cape Cod. Most of Route 6A is also known as the Old King's Highway. Combining the 2 major sections, the highway is approximately 62 miles (100 km) long.

U.S. Route 6 (US 6) in Massachusetts is a 117.952-mile-long (189.825 km) portion of the cross-country route connecting Providence, Rhode Island, to Fall River, New Bedford, and Cape Cod. In the Fall River and New Bedford areas, US 6 parallels Interstate 195 (I-195). On Cape Cod, US 6 is a highway interconnecting the towns of the area. The freeway section in this area is also known as the Mid-Cape Highway. The highway is also alternatively signed as the "Grand Army of the Republic Highway".