Objective：To investigate the relationship between 11 beta-hydroxysteroid dehydrogenase type 1（11beta-HSD1） and preadipocyte differentiation. Methods：The mouse 11beta-HSD1siRNA plasmids were transfected into 3T3-L1 cells for the examination of the effect of targeted 11beta-HSD1 inhibition on differentiation of 3T3-L1 cells. Differentiation was stimulated with 3-isobutyl-1-methyxanthine（MIX）, insulin and dexamethasone（DEX）. Oil Red O staining was used to observe the lipid accumulation. The genes expression was detected by real-time PCR and Western blot. Results：Lipid accumulation was significantly inhibited in cells transfected with mouse 11beta-HSD1-siRNA compared with untransfected 3T3-L1 cells. Fewer lipid droplets were detected in transfected cells both prior to stimulation and after stimulation with differentiation-inducing reagents. The expression of adipocyte differentiation-associated markers such as lipoprotein lipase（LPL）， fatty acid synthetase（FAS） were downregulated in transfected cells. Similarly, the expression of preadipocyte factor-1（Pref-1）, an inhibitor of adipocyte differentiation, was downregulated in transfected cells stimulated by MIX, insulin and dexamethasone. Conclusion：11beta-HSD1 can promote preadipocyte differentiation, and may be an important candidate mediator of obesity and obesity-induced insulin resistance.