Background: Staphylococcus aureus is one of the most important pathogens and the cause of suppuration, abscess formation, a variety of pyogenic infections, and even fatal septicemia in human beings. Isolation of resistant strains of S. aureus especially meticillin-resistant one has elucidated the importance of finding new antibacterial agents. Sumac is one of the important medicinal herbs of Iranian traditional medicine (ITM). Sumac has been traditionally prescribed for some ailments with infectious etiology and therefore, it probably contains antibacterial compounds. Recently, antibacterial activities of sumac against some bacteria were studied by our team. Objective: In this article, we aimed to compare the antibacterial activities of sumac against meticillin susceptible (MSSA) and meticillin resistant S. aureus (MRSA) via minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) determination. Materials and Methods: Antibacterial activity of sumac water extract was studied on 19 clinical and 1 standard strain of S. aureus via MIC and MBC determination. Based on their sensitivity to cloxacillin, these bacteria were classified as meticillin-susceptible, intermediate meticillin-resistant, and meticillin-resistant. MICs and MBCs of the extracts in these 3 groups were statistically compared via one-way analysis of variance (ANOVA) followed by a post hoc analysis (Tukey HSD test) using SPSS for Windows (version 15). Results: The results showed that in spite of different susceptibilities to cloxacillin, susceptibility to sumac extract was not different and MICs and MBCs of sumac for all clinical isolates including MSSA and MRSA were similar (P > 0.05). Conclusion: Based on previous studies, sumac extract acts against S. aureus probably through changing the cell wall properties. This activity is similar for both MRSA and MSSA. More investigation on the precise mechanism of action of this extract would be fruitful.