The　organic　Rankine　cycle　is　a　mature　small-scale　power　generation　technology　for　harnessing　low-　to　mid-temperature　heat　sources.　However,　the　low　efficiency　of　the　cycle　still　hinders　its　widespread　implementation.　To　optimize　the　cycle＇s　performance,　it　is　crucial　to　identify　the　source　and　magnitude　of　losses　within　each　component　of　the　cycle.　This　study,　thus,　aims　to　investigate　the　irreversible　losses　and　their　effect　on　the　performance　of　the　system.　A　prototype　organic　Rankine　cycle　(ORC)　with　the　exhaust　of　a　diesel　engine　as　the　heat　source　was　developed　to　experimentally　investigate　the　system　and　ascertain　the　losses.　The　experiments　were　performed　at　steady-state　conditions　at　different　evaporation　pressures　from　1300　kPa　to　1600　kPa.　The　exergy　loss　and　exergetic　efficiency　of　the　individual　component　and　the　overall　system　was　estimated　from　the　experimentally　measurement　of　the　pressure,　temperature,　and　mass　flow　rate.　The　results　indicate　that　the　exergy　losses　of　the　evaporator　are　almost　60　kW　at　different　evaporation　pressures　and　the　exergy　loss　rate　is　from　69.1%　to　65.1%,　which　accounted　for　most　of　the　total　exergy　loss　rate　in　the　organic　Rankine　cycle　system.　Meanwhile,　the　highest　shaft　efficiency　and　exergetic　efficiency　of　the　screw　expander　are　49.8%　and　38.4%,　respectively,　and　the　exergy　losses　and　exergy　loss　rate　of　the　pump　and　pipe　are　less　than　0.5　kW　and　1%.　Due　to　the　relatively　higher　exergy　loss　of　the　evaporator　and　the　low　efficiency　of　expander,　the　highest　exergetic　efficiency　of　the　organic　Rankine　cycle　system　is　about　10.8%.　The　study　concludes　that　the　maximum　improvement　potential　lies　in　the　evaporator,　followed　by　the　expander.