A toy for pets includes a supporting frame, an annular frame, and a running ball. The rods extending respectively from the two opposite ends of the central axis of the running ball are inserted respectively into a pair of opposite holes in the inner periphery of the annular frame to pivotally connect the running ball to the annular frame. The rods extending inward from the two lateral sides of the supporting frame are inserted respectively into a pair of opposite holes in the outer periphery of the annular frame to pivotally connect the annular frame to the supporting frame, wherein the two pairs of holes are angularly offset from each other. A pet running in the running ball can generate a driving force that changes the direction of the running ball and of the annular frame and thereby changes the running direction of the pet itself
