In last decade, there has been increasing interest about fuel cell-heat engine or refrigerator hybrid systems. Molten carbonate fuel cells (MCFC) provides an opportunity to be used in a hybrid system because of high temperature heat obtained from the system. Brayton cycles may be an alternative to use with MCFC as bottom cycle. In this paper, - MCFC-supercritical CO2 (SCO2) Brayton cycle hybrid heat engine is investigated as a promising power generation option. SCO2 Brayton cycle is chosen because of some advantages like higher efficiency comparing with conventional (air) Brayton cycle. This hybrid system is investigated ecological criteria involving ecological function and exergetic sustainability index as well as basic thermodynamic parameters. Results are obtained numerically and performance limits are tried to define for designing more environmental friendly system. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.