Heat transfer enhancement has been used widely in recent years. It results in heat exchangers to work at a lower fluid velocity and also reduction of driving force temperature and decrease in size of heat exchangers too. Many ways exist to achieve these goals. One of them is utilization of inserts. Both heat transfer and pressure drop increase by using of inserts. There are many types of inserts, like twisted tape, wire coil, wire mesh, etc. In this study the effect of inclined inserts on enhancement of heat transfer and pressure drop is investigated. A Performance Evaluation Criterion (P.E.C) is introduced to evaluate the performance of these insert. In this project, effect of inclined inserts on heat transfer and pressure drop in a single shell and tube heat exchanger is investigated. Steam is used as a heat source to obtain a uniform wall temperature and the working fluid in the tube is water. The inserts used in this project divide in two forms .Some of them are solid inserts and some are inserts whit a hole. In solid inserts the fluid, water, passes between the inserts and wall of tube. The second form of inserts is a circular disk with a hole in different shapes, in this case fluid passes through the hole. Another important parameter which is studied is the shape of the inserts. The shape of the solid inserts or the shape of the hollow inserts can be square, rectangle, circle, or elliptic. Angel of inserts relative to axis of pipe and angle of insert relative to each other are studied. The angel between insert and pipe’s axis is shown by ? and the angel of inserts relative to each other is shown by ?. The effects of these parameters on heat transfer and pressure drop are investigated in this study for different Reynolds numbers. The results of experimental tests have shown that these inserts cause heat transfer and pressure drop to enhance. They have shown that inserts with a hole perform better than solid inserts. They also have demonstrated that ? = 45 0 is the best angel for inserts however there is no judgment for best ? angle. It seems that the best ? angel depends on Prandtl number and shapes of inserts. The highest P.E.C achieved was 1.85 which corresponds to inserts with rectangular hole at ? = 45 0 and ? = 0 0 .for this case, the nusselt number increased by a factor of 2.31. Key words: internal flow, inserts, enhancement of heat transfer.