In this investigation the experiments carried out to determine performance of ?Al 2 O 3 /water and TiO 2 /water nanofluids in a shell and tube heat exchanger. The experiments were done for a wide rang of volumetric concentrations of nanoparticles as well various flow rates of nanofluids. The overall heat transfer coefficient, forced convection heat transfer coefficient, Nusselt number and pressure drop were measured and calculated for both aforementioned nanofluids. For both nanofluids an optimum nanoparticle concentration exists which possesses the most heat transfer enhancement. The optimum nanoparticle concentration for ?Al 2 O 3 /water nanofluid is 0.5% and for TiO 2 /water nanofluid is 0.3%. Thermal characteristics of 0.3% TiO 2 /water nanofluid is greater than ?Al 2 O 3 /water at a certain Peclet number while at higher nanoparticle concentration ?Al 2 O 3 /water suspention possesses beter thermal behavior. The experimental results and available theoritical correlation are in good agreement in low concentration. Variation of pressure drop of nanofluids with various nanoparticle concentrations in a certain volume flow rate is very small but the variation is significant for conctant Reynolds number.