An air compressor with enhanced air compressing effect comprises a mounting chassis with a coupling aperture, a piston having a piston rod with a crankpin linking bore and a piston head with an air acting face, a cylinder having an air chamber with an inner top wall, and a driving mechanism including a motor having a shaft and a rotational crank cam with an eccentric crankpin. The coupling aperture on the mounting chassis is bias disposed relative to the axial line of the cylinder. Both of the air acting face on piston head and inner top wall in cylinder are configured into corresponding slant planar surface. The eccentric crankpin on the crank cam pivotally links the crankpin linking bore on the piston rod of the piston so that rotary motion of the crank cam is converted into linear reciprocating motion. Thus, air compressing effect is substantially enhanced.