This communication presents an investigation of a finite time thermodynamic analysis of an endoreversible Stirling heat engine. Finite time thermodynamics has been applied to maximize the power output and the corresponding thermal efficiency of an endoreversible Stirling heat engine with internal heat loss in the regenerator and for the finite heat capacity of the external reservoirs. The effect of the effectiveness of the various heat exchangers, the inlet temperatures of external heat reservoirs on the power output and the corresponding thermal efficiency have been studied. It is seen that an endoreversible Stirling heat engine with an ideal regenerator (epsilon(R)=1.00) is as efficient as an endoreversible Carnot heat engine. It is also found that the maximum power output increases with the heat capacitance rates and effectiveness of the source/sink side heat exchangers while thermal efficiency increases with the effectiveness of the regenerator.