In this paper, energy, exergy and economic evaluation of a single cylinder diesel engine fuelled with diesel fuel and two types of biodiesel-diesel fuel blends (i.e., B10 and B50) were conducted by evaluating experimental data. Experiments were carried out at five different engine speeds and full load conditions. Energy and exergy components of the engine were calculated and compared for each operating conditions and test fuels. Results obtained from biodiesel-diesel fuel blends were found to be better than neat diesel fuel in respect of both energy and exergy analysis. The maximum brake thermal efficiency and exergy efficiency of the test engine were found to be 40.41% and 37.83%, respectively, at 2000 rpm for B10. Also, the minimum exergy destruction occurred at 2000 rpm for all test fuels. However, from the point of specific fuel costs, B10 and B50 gave quite higher economic costs in compared to diesel fuel. Since fuel price per litre of biodiesel is quite higher than diesel fuel, higher biodiesel rates in the blend dominate increase in specific fuel costs even specific fuel consumption decrease.