Nowadays nanofluids are widely used for heat transfer enhancement. Nanometer-sized particles added to base fluid enhance the thermal conductivity and thus increase the heat transfer rate. In the present study TiO 2 nanoparticle with the average diameter, 21 nm is used. Titanium dioxide (TiO 2 ) nanofluid prepared by dispersing nanoparticles in distilled water using the two- step method with volume concentration (0.05% - 0.3%), has been investigated. The force convective heat transfer coefficient and friction factor of the TiO 2 /Distilled water nanofluid with different volume concentration and Reynolds number for flow in a counterflow double tube heat exchanger are studied in this research. The result shows that the convective heat transfer coefficient of nanofluid is higher than base fluid for the same mass flow rate and same inlet temperature of nanofluid. The Nusselt number increases with Reynolds number and volume concentration TiO 2 /Distilled water of nanofluid. Meanwhile, micro-fin tube increases pressure drop in the flow path.