Abstract: Nine monoclonal antibodies against L. donovani Xinjiang strain were obtained by fusing Sp2/0 myeloma cells and spleen cells from immune mice with a fusion rate of 91.7%. ELISA showed that the antibody tilers produced from 7 recloned McAbs ranged from 1:12,800 to 1:819,200. Among them, McAbs E12 and A11 exhibited certain in vitro protective effects and were characterized as:1. The antibody titres of both E12 and A11 were 1:51,200; 2. Protein contents(mg/ml) were 110.7 and 64.2, respectively; 3. Both belonged to IgG2b subclass; 4. On incubation of living promastigotes of L. donovani Xinjiang strain with the McAbs and complement, strong agglutination resulted. Under electron microscope, these promastigotes showed different changes as compared with the controls, such as rarefaction of cytoplasm, increase of cellular vacuoles in size and number. Adhesion between promastigotes was also found, suggesting that E12 and A11 may have protective effects against the promastigotes.