The　evaporator　is　a　critical　component　when　using　organic　Rankine　cycle　(ORC)　to　recover　waste　heat　from　an　internal　combustion　engine.　Evaluating　the　amount　of　heat　quantity　that　can　be　transferred　in　a　designed　evaporator　is　very　important　for　a　successful　ORC　system.　In　this　paper,　a　finned　tube　evaporator　used　for　recovering　the　exhaust　waste　heat　of　a　diesel　engine　was　presented.　The　mathematical　model　for　the　evaporator　was　set　up　according　to　the　dimensions　of　the　designed　evaporator　along　with　the　specified　working　conditions　of　ORC.　The　evaporator　performance　was　analyzed　as　the　matched　diesel　engine　operating　at　the　rated　power　point.　The　results　indicate　that　the　heat　transfer　quantity　of　the　designed　evaporator　can　be　reached　at　76　kW,　and　the　exhaust　temperature　at　the　evaporator　exit　can　be　reduced　to　115&.　©　(2012)　Trans　Tech　Publications,　Switzerland.