OBJECTIVE: To study the effect of dexamethasone (DXM) on the proliferation of rat glomerulus mesangial cells (GMCs). METHODS: The GMCs lines of the rat were cultured in virto. Both DXM and lipopolysaccharide (LPS) or LPS alone were added into the culture medium (DXM group or LPS group); in the others, neither DXM nor LPS was added and they were used as controls. The GMCs proliferative level was detected by the MTT method at 24 and 48 h of the experiment. RESULTS: The GMCs proliferative level in the DXM group of 4 000 ng/well at 48 h [( 0.251 ± 0.056 ) ng/L] was lower than that of the LPS group [( 0.787 ± 0.110 ) ng/L] and the controls [( 0.678 ± 0.101 ) ng/L](P< 0.05 ); and the GMCs proliferative inhibition reached a peak at 48 h. CONCLUSIONS: DXM may inhibit the proliferation of GMCs in rats.