This paper is concerned with the selection of proper working fluids for medium temperature range heat pipe. The heat pipe which is made of SUS 316L has a total length of 700 mm as well as an outside diameter of 27.2 mm and a thickness of 2.1 mm respectively. Working fluids used in this study were Naphthalene, Biphenyl and Dowtherm A. Their charge amounts were about 40% of the inside volume of evaporator section. Experimental results shows that the Dowtherm A is good for $200^{circ}C{sim}300^{circ}C$temperature range, while the Naphthalene is proper for $300^{circ}C{sim}430^{circ}C$. In the case of the Naphthalene heat pipe, the heat transfer rate reaches 1500 W along with a vapor temperature of $430^{circ}C$.