Nano lubricants are a special type of fluids which are mixtures of nano particles and lubricants. The addition of nano particles to the lubricant, results in improvement of the thermo physical properties and heat transfer characteristics of the lubricant. Thereby improving the performance of the refrigeration system. R134a is most widely used refrigerant in refrigeration equipment, such as domestic refrigerators and air conditioners. Nano fluids are prepared by suspending nano sized particles (1-100nm) in conventional fluids and have higher thermal conductivity than the base fluid. In present work nano particles of CuO at different proportions (with volume fraction 0.1, 0.2 and 0.3% by mass) are dispersed in POE lubricant and in VCR system for better performance. The COP of vapour compression refrigeration system is improved by increasing the refrigeration effect in terms of cooling load capacity and by reducing work done. Result shows that COP of experimental system is increased by