Objective: To study proliferation and biological functions of 4-1BBL reverse signals in the primary blast cells of human acute myeloid leukemia(AML). Methods: Twenty-six AML patients were enrolled. The expression of 4-1BBL protein was detected by FACS in human primary AML cells. Anti-4-1BBL mAb(1F1) was used to stimulate primary human myeloid blast cells. Cell proliferation was determined using Alamar Blue assay. The production of cytokine matrix metalloproteinase 9(MMP-9) in the culture supernatants of AML cells. was determined by a cytokine-specific ELISA. Results: FACS analysis showed that 4-1BBL molecule was constitutively expressed on AML cells. Among the 26 cases,46.15% expressed 4-1BBL molecule. Anti-4-1BBL mAb 1F1 stimulated the proliferation of 4-1BBL positive AML cells. The level of MMP-9 in the culture supernatants of AML cells treated with 1F1 and isotype IgG1 for 48 hours were(965.06 ± 229.94) pg/ml and(596.49 ± 129.28) pg/ml,respectively(P < 0.01). Conclusion: 4-1BBL molecule is constitutively expressed on human AML cells. 4-1BBL reverse signaling plays a critical role in AML cells survival and growth,and contributes to MMP-9 release.