The present invention relates to a weight-balancing structure for rotary polygon mirror of color laser printer, 1 which includes a stator set, a rotor set having a loading disc fixed on a spindle, a motor housing disposed underneath the loading disc, and a rotary polygon mirror is fixedly integrated with the loading disc with a spring member. The spring member has a plurality of spring paws disposed around the circumference thereof and obliquely extended in a downward direction. At least two spring paws are further integrally formed with a ring portion, and the ring portion is located around the outer circumference of each spring member and formed to curl in an upward direction. The weight block could be stuck on the inner periphery of the ring portion by an adhesive-applying means so that it won't come off while positioned in an environment of high rotation speed.