Abstract: Objective To investigate the effects of mCD99L2 gene silencing on the mice B lymphoma cell line A20 transferred to H/RS-like cells. Method Recombinant plasmid LV-mCD99L2 was transfected into A20 cells which endogenetically express mCD99L2. The stably expressed cell line was selected by Blasticidin. The expression of CD30 in transferred cells was detected by immunofluorescense and FCM method. Observation of A20-LV-mCD99L2 cells was applied by transmission electron microscope. The proliferation of the tumor cells (the diameter of H/RS-like ≥25μm) of A20- LV- mCD99L2 and A20 in vitro and in nude mice was examined by continuously cell counting, and taken the human Hodgkin lymphoma cell line L428 as control. The cell cycle was detected by FCM method. Result Stable expression cell clone A20-LV- mCD99L2 was obtained after recombinant plasmid transfection. The expression of CD30 in transferred cells was positive, and the rate of expression of CD30 in A20-LV- mCD99L2 was 54.4%. The observation of transferred cells showed that the cells nuclear were larger and H/RS-like cells with obvious nucleoli which were uninucleated, binucleated and multinucleated cells. The result of cell counting showed that the rate of H/RS-like cells of A20-LV-mCD99L2 was obviously higher than that of A20（P<0.01）in vitro and in vivo. Cell cycle analysis showed that no obvious differences between A20-LV- mCD99L2 and A20 in S stage and no obvious apoptosis was detected in A20-LV- mCD99L2 and A20. Conclusion mCD99L2 gene silencing may transfer mice B lymphoma cell line A20 into H/RS-like cells in vitro and in vivo.