Abstract: Objective To investigate the impact of MDR1-targeting small interfering RNA (siRNA) on the proliferation of OCI-LY1 cells in diffuse large B-cell lymphoma. Methods A20 gene was silenced using RNA interference. An optimal concentration and treatment duration of vincristine were selected using MTT. Before and after siRNA transfection, proliferation of OCI-LY1 cells were assayed using MTT assay, and cellular apoptosis was detected using FCM before or after the treatment of the cells with VCR. Detection of A20, NF-κB (p65) and Pgp proteins were conducted using Western blotting whereas mRNA of the A20 and MDR1 genes were examined using real time PCR. Results 1. Proliferation of OCI-LY1 cells was enhanced (P<0.001) after the transfection with siRNA-2,(P<0.05). In addition, cell proliferation curve was declined after VCR stimulation, but the decrease was slower in siRNA-transfected cells than the untransfected counterparts. 2. Apoptostic rate was lower in siRNA-transfected cells than the untransfected counterparts, and the rate was higher in the cells after treatment with the drug for 24h (P< 0.05). Increased apoptosis was more obvious in common OCI-LY1 cells than in siRNA-transfected cells after the treatment with VCR(P<0.05). 3. The expression of MDR1 mRNA and Pgp (P <0.001) was significantly increased after transfection, but the expression of MDR1 mRNA and Pgp were significantly decreased (P<0.05). The expression in VCR group was significantly lower than that in siRNA-transfected cells+VCR group (P<0.01).C onclusion A20 siRNA could effectively enhance NF-kappa B expression in OCI-LY1 cells. NF-kappa B may up regulate the expression of its downstream genes such as MDR1 and cause apoptosis, in turn enhancing the inhibition of cell proliferation. VCR can reduce MDR1 mRNA and Pgp expression in OCI-LY1cells and the effect of VCR could be attenuated by A20 siRNA.