The hand truck brake provides automatic braking for a hand truck as it negotiates a stairway or other uneven surface. The brake is adaptable to various types of hand trucks, including powered stair-climbing trucks. The brake includes two major assemblies. The first is a reciprocating plunger having a distal roller that travels along the surface. When the roller travels over the nose of a stairway tread, the plunger extends to actuate the brake. The second major assembly is a rotary cam rotated by the plunger as it extends. The cam has an extension and a brake shoe, the brake shoe engaging the underlying surface to stop the hand truck when the cam is rotated to its brake-engaging position. The assembly automatically retracts when the hand truck is oriented vertically. Additional controls are provided for the operator to extend or retract the brake mechanism.