An hinge auto-return device for a glass door includes a body containing a longitudinal pivot hole to rotatably receive a pivot pin in the body and a lateral guide hole to movably receive a positioning block in the body. The lateral guide hole extends perpendicular to communicate with the pivot hole. At least one blind hole is longitudinally defined in the positioning block to mount at least one resilient member in the positioning block. The positioning block has a contact face forced by the resilience of the resilient member to press against a flat segment of the pivot pin when a hinge assembled with the auto-return device is attached to a glass door and hinges the glass door on a doorframe. The positioning block is able to slide smoothly in the guide hole in the body of the auto-return device so that the auto-return device performs reliably and durably.