The present invention provides a light emitting diode lamp, which includes at least a light emitting diode and a control circuit. The light emitting diode lamp has an anode pin, a cathode pin, and a synchronous pin. The anode pin and the cathode pin receive a DC voltage, and the synchronous pin is connected to the control circuit. Moreover, the present invention provides a synchronous light emitting diode lamp string, which includes a plurality of light emitting diode lamps and at least a power adapter. Each light emitting diode lamp has a synchronous pin, and all synchronous pins are connected together. The control circuit can control the color changing of the light emitting diode based on a reference signal from the synchronous pin.