Coconut oil is one of the organic PCM materials with high thermal energy storage capability in the form of sensible and latent heat. Ideally, the latent heat storage occurs at a relatively constant temperature associated with phase change transition. Due to relatively low thermal conductivity, the size effect is important to optimize material performance, particularly at the discharging process related to latent heat release. This study will show the simulation results of the size effect in the solidification process of coconut oil by using ANSYS FLUENT. Three plastic balls with radii 2 cm, 3 cm, and 6 cm filled with coconut oil solidified from 308 K to 293 K, and several temperature detectors were placed in the ball to study the heat exchange process. The input parameters of density, heat capacity, thermal conductivity, and viscosity were taken from previous experimental studies. We reported the time evolution of temperature and liquid fraction until the molten coconut oil solidified from different detector positions in each ball.