For　displacement　expanders,　the　irreversible　losses　include　leakage,　friction,　heat　dissipation,　and　flow　resistance.　Currently,　the　research　on　the　heat　loss　of　expanders　is　scarce,　especially　with　regards　to　experimental　studies.　In　this　paper,　the　experimental　research　on　the　heat　loss　of　the　single　screw　expander　(SSE)　for　the　Organic　Rankine　Cycle　was　carried　out　under　different　working　conditions,　in　the　summer　and　winter,　respectively.　In　each　set　of　experiments,　there　were　five　cases,　and　the　temperatures　of　the　working　fluids　at　the　inlet　of　the　expander　were　83,　93,　103,　113,　and　123　degrees　C,　respectively.　The　heat　removed　by　the　lubricating　oil　was　also　measured　throughout　the　experimental　period.　The　experimental　results　showed　that　the　amount　of　heat　loss　was　not　comparable　to　the　output　power　and　enthalpy　difference　between　the　inlet　and　outlet　of　the　SSE.　The　proportion　of　the　heat　dissipated　by　the　casing　was　only　30%　ranging　from　0.11　to　0.28　kW.　Comparing　the　experimental　results　in　summer　and　winter,　the　heat　loss　in　summer　was　lower　than　in　winter,　but　the　variation　in　output　power　showed　an　opposite　trend.　It　was　also　shown　that　heat　loss　was　not　a　main　factor　affecting　the　performance　of　SSEs.