SR 25 Business begins at the intersection of William Clarke Drive (SR 25), Main Street, and New Gorham Road in Westbrook. The two routes run parallel to one another for about a mile, with SR 25 running on William Clarke Drive and SR 25 Business running on Main Street. The routes continue this way until reaching the Westbrook Arterial, which SR 25 turns onto to bypass the city to the south, towards the Maine Turnpike. SR 25 Business continues through Westbrook along Main Street, turning southeast to continue on Main Street in the middle of the city.