By this study, it is aimed to improve the thermal performance of the two phase closed thermosyphon (TPCT) using nano fluid that contains TiO2 particles. The heat pipe utilizing in this work had 1 m length. Its inner and outer diameters were 13 mm and 15 mm, respectively. While both the evaporator and the condenser sections had 400 mm length, the rest 200 mm length of the pipe consisted of adiabatic section. In experimental study performed, one third of the overall volume of the heat pipe was filled with working fluid. In order to determine the heat amount extracting from the condenser section, 3 different mass flow rates of cooling water (5 g/s, 7.5 g/s and 10 g/s) was used. The experiments, in addition, were completed for 3 varied heater power (200 W, 300 W and 400 W) for evaporating the working fluid. They were conducted separately not merely for the water, but also the nano fluid and the findings were compared to each other. The best result was acquired from the experiment in which working fluid was nano fluid with the cooling water mass flow rate of 5 g/s and 200 W heater power.