Recently, applications of nanofluids for enhancment of heat transfer performance of thermal systems have been improved. There are many published works dealing with studies of nanofluids heat transfer in very simple geometrical configurations (e.g. circular channels and tubes). But there are a few published experimental and numerical works related to heat transfer of nanofluids in the heat exchangers. In this study, heat transfer of the ?-Al2O3/water nanofluid with 0.2% and 0.5% volume fractions, flowing in double pipe, shell tube and plate heat exchangers counter flow under laminar flow conditions investigated experimentally. Effects of hot and cold mass flow rates, temperature and nanoparticle volume fractions on the overall heat transfer coefficient and heat transfer rate of the nanofluids have been investigated. Furthermore, ?-Al2O3/water nanofluid with 0.2% and 0.5% volume fractions was used in plate heat exchanger to evaluate the nanofluid type effects on the forced convective heat transfer. Finally the performance of heat exchangers is compared together.The results of the experiments showed that the heat transfer rate and overall heat transfer coefficients of nanofluid are higher than those of the base fluid (distillated water) and overall heat transfer coefficient increases with increasing the nanoparticles concentration. Also heat transfer rate and overall heat transfer coefficients of nanofluid increase with an increase in the flow rate of the nanofluid and cold water, and nanofluid temperature in all of the heat exchangers. Compared with pure water, the results indicated that the heat transfer performances of nanofluid with 0.5% nanoparticle volume concentrations in the double pipe, shell tube and plate heat exchangers are higher than those of water by about 7.6%, 12.7% and 16.9% respectively. In plate heat exchanger overall heat transfer coefficient of ?-Al2O3/water nanofluid with respect to ?-Al2O3/water was more in the same concentrations. The average increasing in the overall heat transfer coefficient of ?-Al2O3/water nanofluid with respect to ?-Al2O3/water with 0.2% and 0.5% volume fractions was 5.6% and 4.4% respectively. The overall heat transfer coefficients of nanofluid in the plate heat exchanger are higher than shell tube heat exchanger and in the shell tube heat exchanger is higher than double pipe heat exchanger. The average increasing in overall heat transfer coefficient for ?-Al2O3/water nanofluid with 0.5% volume fraction in 50?C, for plate heat exchanger with respect to shell tube heat exchanger is 29.9%, and for shell tube heat exchanger with respect to double pipe heat exchanger is 22.8%.Simulation of double pipe and shell tube heat exchangers carried out by means of the processes in FLUENT version 12.1 numerically. The GAMBIT software has been used for geometry and mesh generation. The overall heat transfer coefficients predicted by CFD simulation were compared with the experimental results. It was observed that the CFD results are in the good agreement with experimental data. In nanofluid with 0.5% concentration, the average relative error between experimental data and CFD results for the double pipe heat exchanger is 11.7% while for the shell tube heat exchanger is 15.6%. It is shown that the computational fluid dynamics is a reliable tool for investigation of heat transfer of nanofluids in the various kinds of heat exchangers. Key words: nanofluid, heat transfer, overall heat transfer coefficient, heat exchanger, simulation