An air compressor has a housing, a battery, a printed circuit board, a switch, an air compressing device and a belt. The housing is composed of a right cover and a left cover. A battery chamber, a printed circuit board chamber and a compressing device chamber are defined between the right and left covers to respectively receive the battery, the printed circuit board and the air compressing device. A baffle is formed in the housing between the printed circuit board chamber and the compressing chamber. The switch is mounted in and exposed from the housing and electrically connected to the printed circuit board. The belt is attached to the housing, such that a user can conveniently and easily carry the air compressor on the user's body to any desired location for use.