Abstract: In this research the effect of copper oxide nanofluid ( pure water mixed with copper nanoparticle with 30-50nm diameter ) on the thermal efficiency enhancement of a heat pipe at different operating state was investigated . The heat pipe made of straight copper tube of outer diameter 12 mm and inner diameter 10 mm. The tested concentration level of nanofluid are 0.3, 0.6, 0.9wt%. This study presents the discussion on the effect of coolant rate, inclination angle of solar collector and effect of nanomaterial concentration on the performance of solar collector. Result shows that by charging the nanofluid to the heat pipe the thermal performance is enhanced. Performance of solar collector was increases with increase in inclination of solar collector and concentration of nanofluid up to certain level and then again decreases. Increase in coolant rate also increases the thermal performance up to certain level.