Abstarct: Performance of heat transfer systems has been considered in past recent years. This attention guided investigations to using of new methods. For this purpose, various techniques have been proposed as the use of nanofluid and curved tubes. New studies were started at applications of nanofluids and curved tubes. Experimental investigation of force convective heat transfer of nanofluids in curved tubes has not been considered in the literature and challenge is considered to be an open research topic that may reqire more study. This thesis is one of the first works which focuses on nanofluids flow and heat transfer in curved tubes experimentally. Forced convective heat transfers of nanofluid were done in curved tubes with constant wall tempreture boundry condition in Reynolds numbers, i.e. 400<Re<2200. Alumina nanofluid in volume fraction of 0.1% for uniform wall temperature that made by two step method and basic fluid (water) and three tubes with the curvatures of 0.116, 0.074 and 0.042 with equal outer surface area of same material are used for this experiment. Tube inlet temperature is constant in during the test is considered. Measurement of temperature and pressure drop of nanofluid along with test section is done at each test. Results along with statical method, the confidence intervals, with 95% accuracy were reported. Also for validate the pressure test data; formula for curved tubes was used. The result of this comparsion was shown an expectable error from correlations. Maximum increase of nusselt number for curved tubes with 0.042, 0.074 and 0.116 curveture are 15%, 13% and 12% respectively for the nanofluids compared to the basic fluid. Also result shows maximum a significant increase of nusselt number versus curve tube with 0.116 curveture ( maximum increase of 22% and 45% for curve tubes with 0.074 and 0.042 curvetures respectively) at Re=1300. The results shows maximum absorbed heat nanofluid for curved tubes with 0.074 and 0.042 curvetures are 4.7 and 1.15 respectively versus curve tube with 0.116 curveture .