The present invention discloses a mobile device positioning structure including, a central magnetic portion on a mounting surface of a fixture for magnetically positioning the back of a mobile device and a ring-shaped magnetic portion formed by two curved clamp arms which are bilaterally symmetrical to each other, and separated and unfolded from each other. After the two curved clamp arms are unfolded relative to the mounting surface, the back of the mobile device is magnetically positioned by the central magnetic portion, and both sides of the mobile device are elastically abutted, clamped and positioned by the two curved clamp arms.