An automatic pet food dispenser at preset times and for a definite quantity includes a dispenser body, a food storing tank, a funnel-shaped receiver, a transporting mechanism. The transporting mechanism consists of a food pipe and a screw conveyer deposited in the food pipe and rotated by a motor for transporting pet food by the screw conveyer to let the food fall down from the storing tank, through the funnel-shaped receiver, and a timer for presetting times of start and stop and thus the period of operating time of the motor. The dispenser body has a food exit formed in a bottom wall and connected to the lower end of the food pipe, and a food trough movably provided in the bottom portion of the dispenser body to pulled out thereof to receive pet food falling down from the food exit.