An automatically rotatable lamp ball includes a power unit provided with a motor having its downward shaft driving two rollers to rotate and its upward shaft driving a lamp arm to rotate. The lamp arm is disposed thereon with a plurality of LEDs, and the integral body of the power unit and the lamp arm is received in the interior of a transparent outer casing and actuated to rotate therein for pushing the outer casing to roll freely at the same time. When the lamp arm is actuated to rotate, the LEDs installed thereon will simultaneously give out flickering lights in sequence and at intervals and, due to visual persistence, presenting freely movable stereoscopic light patterns or letters. So the invention is innovative and exclusively original in structure and having excellent entertaining effect.