A novel concept of LED street lamp liquid cooling system was proposed in the present study to replace the conventional direct air cooling systems. A micro heat exchanger was attached on the LED chip at the top of the stand. A micro centrifugal pump was installed at the bottom of the lamp stand to drive cooling water through the micro heat exchanger to remove heat that generated from the LED chip. Heated water flew through the lamp stand and dissipated heat from the surface of the lamp stand to the atmosphere by natural convection heat transfer. The lamp stand was used as the heat sink. No heavy fin array was required on the lamp head. The test results show that the maximum temperature at the center of the LED chip is low enough for keeping LED at high performance. The weight of the lamp head in the liquid cooling street lamp is only 4~11% of the other systems cooled by fin array.