In　an　organic　Rankine　cycle　(ORC)　system,　the　working　fluid　pump　plays　an　important　role　in　the　system　performance.　This　paper　focused　on　the　operating　characteristics　of　a　multistage　centrifugal　pump　at　various　speeds　and　condensation　conditions.　The　experimental　investigation　was　carried　out　to　assess　the　influence　of　the　performance　of　the　pump　by　the　ORC　system　with　special　attention　to　actual　net　power　output,　thermal　efficiency　as　well　as　back　work　ratio　(BWR).　The　results　showed　that　an　increase　in　the　pump　speed　led　to　an　increase　in　the　mass　flow　rate　and　expand　in　the　operating　range　of　the　outlet　pressure.　The　mass　flow　rate　decreased　nonlinearly　with　the　increase　of　the　outlet　pressure　from　0.22　to　2.41　MPa;　the　electric　power　consumption　changed　between　151.54　and　2409.34　W　and　the　mechanical　efficiency　of　the　pump　changed　from　7.90%　to　61.88%　when　the　pump　speed　varied　from　1160　to　2900　r/min.　Furthermore,　at　lower　pump　specific　speed　the　ORC　system　achieved　higher　thermal　efficiency,　which　suggested　that　an　ultra-low　specific　speed　pump　was　a　promising　candidate　for　an　ORC　system.　The　results　also　suggested　that　the　effects　of　condensation　conditions　on　the　pump　performance　decreased　with　the　pump　speed　increasing　and　BWR　was　relatively　sensitive　to　the　condensation　conditions,　especially　at　low　pump　speed.