Abstract: In this paper, results of a study on effect of DDB, a clinically effective drug in treating hepatitis, on the membrane fluidity of rat liver cells in vitro are described. The results indicate that DDB can increase the fluidity of liver cell membrane. Futhermore, DDB was found to be able to maintain the structure and function of mitochondria by (1) preventing the mitochondrial swelling induced by Triton X-100, (2) increasing the respiratory control ratio and (3) stimulating oxidative phosphorylation (increasing ATP synthesis and Ca²⁺ uptake). These observations are helpful in elucidating the mechanism underlining the therapeutic effects of DDB in treating hepatitis.