In order to meet the continuously increasing demand from industry, electronics, aerospace, automotive and oil and gas refineries, heat transfer equipments should be smaller, lighter and with higher performanc. Heat exchange fluids have an important role in increasing the thermal efficiency. Nanoparticles increases the thermal conductivity of nanofluids, heat transfer rates and imposing the dispersion of nanoparticles in base fluid and accelerates the process of energy conversion from the other point of view, one of the methods to increasing is to use twisted tape in heat exchanger tubes. This may increase the total heat transfer surface in a given volume and also cause an increase in mixing characteristic of flow, leading to enhance heat transfer. The purpose of this study is to experimentally investigate heat transfer enhancement using nanofluids with TiO 2 nanoparticles inside the tubes with twisted tape inserts. To achive this, an experimental aparatus is designed and manufactured to study the effects of different parameters such as mass flow rate, concentration of nanoparticles in suspension and with varying pitch distance of the twisted tapes. The results of the enhanced heat transfer and pressure drops will be presented. This study evaluates the performance of water / TiO 2 nanofluid for enhancing convective heat transfer in a heat exchanger tube with twisted tape inserts. Factors considered include the twist ratio, mass flow rate and the volumetric concentration of nano-particles. Experiments were conducted in a tube with constant wall temperature. The nano-particle volume concentration varies within the range of , and the twisted tape inserts utilize twist ratio of . The Reynolds number variation is within the range of 3000 Re 22000. The measured results revealed that the addition of nano-particles as well as twisted tape inserts enhanced the convective heat transfer for all test cases. Combining the positive effects of both nanofluid and the twisted tape, the convective heat transfer was significantly increased up to 103.45% for the test case with volumetric concentration of 0.5% nanofluid and twist ratio of H / D = 5. However, the addition of nanoparticles to the base fluid has marginally increased the pressure drop coefficient. Appropriate correlations are introduced for the characteristics of the combined TiO 2 /water nanofluid and twisted tape inserts in circular tubes. Keywords: Experimental heat transfer, TiO 2 /water nanofluid, twisted tape, Convection, Constant wall temperature.