Abstract: Objective: To observe the influence of 4-1BBL small interfering RNA (siRNA) on the growth and apoptosis of HL-60B cells.Methods: The siRNA for 4-1BBL gene was designed and synthesized in vitro,and then transfected into HL-60B cells by Lipofectamine;the expression of 4-1BBL mRNA and protein was detected by RT-PCR and flow cytometry,respectively;the proliferative rate of HL-60B cells was determined by methyl thiazoy tetralium (MTT),and the cell apoptosis was analyzed by flow cytometry.Results: After the siRNA for 4-1BBL gene was transfected into HL-60B cells,the expression of 4-1BBL gene and protein decreased,the growth of cells was repressed and the proliferation rate of HL-60B cells decreased.The inhibition rate was (22.1±2.3)% 48 h after transfection;the apoptosis rate increased from (9.8±2.5)% to (32.5±5.1)%.Conclusions: Chemically synthetic siRNA can decrease 4-1BBL gene expression,inhibit cellular proliferation and promote apoptosis in vitro.