In this work, an experimental study is carried out to investigate the effect of adding MWCNT nanoparticles to the heat transfer oil on flow heat transfer and pressure drop characteristics. Thanks to many studies performed in recent two decays on nanofluids. Although usage of nanofluids heat transfer is in preliminary stages, it is necessary to understand mechanisms of enhancing in heat transfer in these studies. Another technique usually have been used for increasing in heat transfer is use of inserted devices such as wire coils in tubes. They show several advantages in relation to other enhancement techniques such as Low cost and Easy installation and removal. Here, the experimental works are carried out for pure base oil and nanofluids flow inside plain tube and wire coil inserted tubes. The wall temperature was maintained constant throughout this study and fluid flow is either laminar flow or low Reynolds number turbulent flow. To provide constant wall temperature, the entire test section is surrounded by saturated water vapor. The fluid flow in the tubes is considered hydrodynamically developed, but thermally is in developing stage. Heat transfer oil is (HT-B) and nanoparticles are of MWCNT type. The heat transfer oil with the nanoparticles with the weight concentrations of 0.1, 0.2 and 0.4% are considered as the working fluid. The experimental study was carried out on six test sections including a circular tube with 1500 mm length, 14.5 mm inner diameter and 15.6 mm outer diameter and five wire coils fitted in the plain tube within a geometrical range of helical pitch 1.12 p/d 2.79 and wire diameter 0.069 e/d 0.097. Base fluid and nanofluids characteristics like density, viscosity, thermal conductivity coefficient and specific heat capacity have been measured by means of accurate apparatuses. The experimental measurements showed that adding nanoparticles to the base fluid would lead to the increase in density, thermal conductivity and viscosity of the base liquid, but specific heat capacity decreases as nanoparticle concentration increases. The maximum increasing of the value of thermal conductivity up to 15.3% is achieved for nanofluid with the highest concentration. The experimental results of the convective heat transfer of flow inside plain tube and wire coil inserted tubes showed that by increasing the flow rate and nanoparticles concentration, the convective heat transfer coefficient is increased. The maximum enhancement of convective heat transfer coefficient of up to 73% and 1014% are obtained for the nanofluid flow with 0.4% wt. concentration for plain tube and wire coil inserted tube, respectively. On the other hand, results obtained for pressure drop in plain tube and wire coil inserted tubes showed that the pressure drop was enhanced by increasing the flow rate and nanoparticles concentration. Furthermore, the performance evaluation of the two enhanced heat transfer techniques studied in this investigation showed that dilute nanofluids have better efficiency. Key Words nanofluid, heat transfer, pressure drop, constant temperature and wire coil inserts.