A dual-direction pump includes two cylinders arranged on opposite sides of a head portion and an inlet return-flow prevention device and a leakproof device mounted between the cylinder and the head portion for avoiding leakage at the juncture between the cylinder and the head portion or leakage induced by reverse flow in one of the cylinders in the case of a single-sided pumping operation in the other cylinder. The head portion has an outlet port to which an outlet return-flow prevention device is mounted. A knob is rotatably mounted to the outlet pot and a nut is fixed to the knob for selectively engaging an inflation valve to avert detachment. The outlet return-flow prevention device prevents reverse or return flow induced in the outlet port in order to reduce resistance caused thereby and enhances pumping efficiency.