Overheating of the high-power light emitting diode (LED) has a dramatic effect on the chip’s lifetime. Heat dissipation for high-power LED is becoming a major challenge for researchers and technicians. Compared with the air cooling method, the liquid cooling method has many advantages and high efficiency because of higher specific heat capacity, density, and thermal conductivity. Carbon nanotubes with remarkable thermal properties have been used as additives in liquids to increase the thermal conductivity. In this work, multiwalled carbon nanotubes nanofluid (MWCNTs nanofluid) was used to enhance heat dissipation for 450 W LED floodlight. MWCNTs nanofluid was made by dispersing the OH functionalized MWCNTs in ethylene glycol/water solution. The concentration of MWCNTs in fluid was in the range between 0.1 and 1.3 gram/liter. The experimental results showed that the saturated temperature of 450 W LED chip was 55°C when using water/ethylene glycol solution in liquid cooling system. In the case of using MWCNTs nanofluid with 1.2 gram/liter of MWCNTs’ concentration, the saturated temperature of LED chip was 50.6°C. The results have confirmed the advantages of the MWCNTs for heat dissipation systems for high-power LED floodlight and other high power electronic devices.