We analyzed a heat engine using clathrate hydrate as its working media and evaluate the performance of this system operated with high and low temperature reservoirs of 295 K and 280 K "OTEC (Ocean Thermal Energy Conversion)" may be a prospective example of the technologies utilizing the small temperature difference for power generation. This heat engine generates mechanical power through the cycle of following processes: hydrate formation at low temperature, pumping of hydrate, isobaric heating of hydrate, hydrate dissociation and adiabatic expansions of dissociated gas and water. The thermal efficiency for Kr, Xe, CH3F, CH2F2 and CH4 hydrates were evaluated. The analysis showed the dominant properties were the enthalpy difference of the working media in the adiabatic expansions, the pressure range in the whole process and the dissociation heat. The thermal efficiency is 2.20% for Kr hydrate and 2.89% for Xe hydrate. While these are slightly inferior to those of Rankine cycle: 3.30% for C2H3F3 and 334% for C3H8, Kr and Xe hydrates are greatly favorable in terms of environmental friendliness. These results indicate the prospects of the hydrate heat engine for the power generation utilizing a small temperature difference as an environment-friendly technology. (C) 2016 Elsevier Ltd. All rights reserved.