A two-dimensional heat transfer model was proposed to numerically investigate the effect of enriching phase change material (PCM) with different kinds of nanoparticles on thermal performance of glazing windows in different seasons of the year. The results were presented in terms of liquid fraction of PCM, inner surface temperature and temperature difference between interior and exterior surfaces of glass window, and their occurrence times. The results showed that adding nanoparticles into PCM can promote the melting and solidification processes, extend the total time of PCM being in the liquid state, and raise the internal surface temperature of glass. However, in summer season, the internal surface temperature decreases and the total melting time respectively reduces by 7 and 1.5 minutes by introducing TiO2 and ZnO nanoparticles into PCM. Furthermore, the introduced nanoparticles do not have the same effect on the thermal performance of the window unit. While the inner surface temperature decreases by 0.82 K in summer by addition of TiO2 to PCM, it increases by 0.84 K in transition season and 0.89 K in winter season by utilizing ZnO nanoparticles. Although the nano-PCM remains in the solid state in winter, the existence of nanoparticles can still increase the inner surface temperature.