Water cooling systems have been widely used due to generation of heat. As technology changes rapidly, there is urgent requirement of new liquid coolant which leads to increment in heat transfer rate. The thermal conductivity and other properties of nanofluids are promised to increase the heat transfer rate. In this study the thermal performances of a minichannel heat sink are investigated experimentally by using pure water, Al2O3-H2O and CuO-H2O nanofluids. The nanofluids including the volume fraction ranging from 0.1 to 0.5 vol% was used as a coolant which are allow to pass through the small channels of a heat sink. The effects of different flow rates of the various coolants on the complete thermal performances of a minichannel heat sink are investigated experimentally. The flow rate was ranged from 30 LPH to 90 LPH as well as Reynolds no. from 257 to 802. The various coolants was passed through a copper made minichannel heat sink. The experimental result shows the higher improvement of the thermal performances using nanofluids as compared to pure water. The heat transfer coefficient by using Al2O3/Water nanofluid was found to enhance upto 31 % more as compared to pure water. On the other hand by using CuO/water nanofluid, heat transfer coefficient was found to enhance upto 29% more as compared to pure water. The nanofluid significantly lowered the heat sink base temperature (about 3 C) by using both the nanofluids as compared to pure water.