Objective： To study the expression and function of 4-1BBL in the cell lines of human hematological malignancies. Methods： The expression of 4-1BBL was detected by FACS analysis and the effects of 4-1BBL molecule in the cell lines of human hematological malignancies were studied by anti-4-1BBL mAb 1F1. Cell proliferation was determined by cell counts manually and 3H-TdR incorporation. Results： FACS analysis showed that 4-1BBL expressed highly in myeloid leukemia cell line U937， HL60 and B Lymphoma cell lines Raji， Daudi. Cell counts and 3H-TdR incorporation assay revealed that mAb 1F1 could induce proliferation of myeloid leukemia cell line U937 and HL60. Conclusion： 4-1BBL molecule is expressed in the myeloid leukemia highly as well as B lymphoma cell lines. 4-1BBL molecule could mediate reverse signal to promote the proliferation of myelocytic leukemia cell line U937 and HL60.