New York State Route 100B (NY 100B) is a 2.88-mile (4.63 km) spur route of NY 100 in Westchester County, New York, in the United States.

Known as Dobbs Ferry Road, NY 100B proceeds northeast through Greenburgh as a two-lane residential street, passing the local Ferncliff Cemetery and bending east into a junction with Park Avenue.

At the east end of the country club, NY 100B crosses into an interchange with the Sprain Brook Parkway.

After the Sprain, the route continues east through Greenburgh, passing more residences and entering an intersection with NY 100A (West Hartsdale Road / Knollwood Road).

Passing south of a large strip mall, the route crosses into a junction with NY 119 (Tarrytown Road) in the center of Greenburgh.