The present invention relates to an antibacterial pharmaceutical composition comprising an Aceriphyllum rossii extract, and aceriphyllic acid A and 3-oxo-12-oleanen-27-oic acid isolated therefrom. The Aceriphyllum rossii extract of the present invention, and aceriphyllic acid A and 3-oxo-12-oleanen-27-oic acid isolated therefrom have strong antibacterial activities against Staphylococcus aureus, methicillin-resistant S. aureus, quinolone-resistant S. aureus, Acinetobacter calcoaceticus, Micrococcus luteus, Bacillus subtilis or Streptococcus mutans, Propionibacterium acnes, thereby being used for the prevention or treatment of pathogenic bacterial and resistant bacterial infections, cariogenic bacterial and acne bacterial infections.