Most of the current air compressors are driven by a slider-crank mechanism consisted of the crank, connecting rod, and piston. Complexity of this mechanism, however, restricts miniaturization of air compressors. In this study, a design based on a new mechanism, a hybrid of cross-slider and scotch-yoke mechanism, is adopted to develop an oil-free, light-weighted air compressor for portable medical devices. By eliminating the connecting rod, the mechanism has several advantages in addition to the obvious weight reduction due to the simpler mechanism such as the longer seal life of the seal between the piston and cylinder (so called Teflon cup) and reduced shaking forces. Cylinder pressure time history is obtained based on the ideal gas behavior and the isentropic process. Shaking forces and motor torque are calculated from the dynamics equation of the air compressor. The flow capacity curve of the air compressor is obtained by considering the effect of the clearance volume. An actual prototype was fabricated and tested to demonstrate the feasibility of proposed concepts.