Abstract: The study investigated the effects of red clover extract (RCE) on mouse T macrophages and lymphocytes in vitro. The cell toxic effect of RCE was estimated by MTT assay. Multiple-fluorescence staining plus flow cytometry were used to detect the effect of RCE on CD69/CD25/CD71 expression of mouse T lymphocytes stimulated by Con A; CFDA-SE staining plus flow cytometry were used to analyze the effect of RCE on proliferation of T lymphocytes activated by Con A; The effect of RCE on nitric oxide (NO) secretion of mouse macrophages stimulated by lipopolysaccharide (LPS) for 24 h was assayed by Griess reagent system. We found that RCE had potent anti-inflammatory effects on mice. RCE had little cell toxic effect on mouse lymphocytes and macrophages. RCE strongly inhibited the excessive production of inflammatory mediators (NO, CD69, CD25, CD71), in a dose-dependent manner, like cyclosporine A injection. RCE could inhibit proliferation of CD3⁺ T lymphocytes. These data suggested that RCE might exhibit anti-inflammatory effect by inhibiting the activation and proliferation of mouse lymphocytes and the NO secretion of mouse macrophages.