The main disadvantage of solar water heater (SWH) using water as thermal energy storage is the system tends to be weight because it has a low energy density. On the other hand, the phase change material (PCM) is a kind of latent energy storage material which has advantages such as high energy density. One type of PCM from the organic group is a paraffin wax. Based on this advantage, paraffin wax allows to be applied to SWH. The aim of this research is to study experimentally the thermal behavior of SWH involving PCM as thermal energy storage in the tank during the charging process. Research conducted using thermosyphon SWH with main components are solar collector with 2 m 2 areas and horizontal tank volume of 60 liters and it is tested outdoor. Paraffin wax is inserted into the pipe-capsule and the pipes are arranged in the tank. Parameters measured were water temperature, PCM temperature, outside air temperature and solar radiation intensity. Thermocouples mounted on either the water or the PCM in multiple locations. The data obtained was used to analyze the thermal behavior of heat storage in the tank. This study showed that the rate of temperature rise of the water and PCM was 0.229 °C/min and 0.230 °C/min, respectively. The heat transfer process in the tank is good enough because there is no significant difference between the rate of temperature rise of the water and PCM.