Nine Propionibacterium acnes (P. acnes) strains resistant to both clindamycin and erythromycin were selected to investigate the inhibitory ability of extracts and isolated compounds from leaves of Cassia grandis L.f to P. acnes. Ethyl acetate extract inhibited all P. acnes strains, with an aseptic ring diameter of 15-25 mm at a concentration of 200 mg/mL and a MIC value of 30 mg/mL. The fraction H:E 1:1 showed the strongest antibacterial activity in the three investigated fractions (H:E 1:1, H:E 1:3 and E 100%) with an aseptic ring diameter of 19.3-23.7 mm at a concentration of 200 mg/mL (tested on three strongest resistance strains) and the MIC value was determined to be 0.3 mg/mL. In three pure compounds isolated from ethyl acetate extract, quercitrin strongest inhibited for P. acnes with a MIC value of 0.2 mg/mL.