B7-H1 (B7 homologue 1, PD-L1), expressed on the surface of tumor cells or antigen-presenting cells in the tumor microenvironment, can suppress antitumor immune reaction, promote tumor growth and help tumor cells to escape the immune response. To investigate the correlations between B7-H1 expression and acute leukemia patients' immunotherapeutic efficacies and prognoses, we detected the expression of B7-H1 by immunohistochemistry and Real-time quantitative PCR and monitored the immunotherapeutic efficacies and prognosis in 60 acute leukemia patients, in which 14 cases of acute monocyte leukemia(M5) patients received active immunotherapy. The levels of mRNA and protein expression of B7-H1 changed synchronously.B7-H1 was expressed in human acute leukemia cells, especially in M5. The expressions of B7-H1 were significantly higher in the relapse patients than in the de novo patients and after immunotherapy than before immunotherapy. Significant correlations existed between the expressions of B7-H1 and the M5 patients' immunological reactions and immunotherapeutic efficacies.B7-H1 negative patients had better immunotherapeutic efficacies than the positive patients who were prone to have a severe complication of pulmonary infection. Multivariate analysis indicated that B7-H1 status was an independent prognostic factor for M5 patients. In conclusion, B7-H1 is highly expressed on leukemia cells of M5 patients, can significantly affect the immunotherapeutic efficacies of M5 patients and is a novel prognostic marker for M5.