The heal capacity of perovskite lead titanate PbTiO3 was measured by differential scanning calorimetry in order to investigate the isotope effect on ferroelectric phase transition. The transition temperature and the shape of the anomaly in the heat capacity curve due to phase transition changed by the Ti-isotope substitution. The phase-transition temperature of Ti-46-enriched PbTiO3 was about 8.8 K higher than that of Ti-49-enriched PbTiO3. The shape of the anomaly in the heat capacity curve became broad with increasing the mean mass of Ti.