An actuator for a syringe is disclosed with which precise liquid quantities can be dispensed in an accurately repeatable manner with single-hand control. The actuator is formed with a main body shaped to support a syringe whose plunger is moved by a plunger actuator. A reciprocating finger actuatable pusher is mounted with the plunger actuator to the main body and a ratchet mechanism operative between the plunger actuator and the pusher provides discrete motions of the plunger actuator. The main components of the syringe actuator are formed of extruded material and shaped in cross section to conveniently fit together. A back motion inhibitor is employed in the form of a fibrous material capable of restraining reverse movement of the plunger actuator while allowing unobstructed operative movement thereof.