The present invention relates to an air inlet structure for a pneumatic tool, in which, an inlet pipe are inserted in the inlet hole of the switch seat of the pneumatic motor and in the through hole of the air chamber of the pneumatic tool, respectively, on the both ends of the inlet pipe are formed with plural grooves for reception of O-shaped rings which are used to prevent air-leakage from clearances between the pneumatic tool and the inlet pipe, and between the switch seat and the inlet pipe.