The present study was carried out to evaluate the antimicrobial activity of ethanol plant extract of rosemary (Rosmarinus officinalis) and / with five antimicrobial agents of different mechanisms (oxytetracycline Hcl, amoxicillin, cefquinome, sulphaquinoxaline and danofloxacin) against field strain of S. aureus. By using agar well diffusion method, the mean zone of inhibition (mm) of ethanol extract of Rosemary were 21.67±0.33, 20.33±0.33, 19.67±0.17, 18.83±0.17, 18.17±0.17, 16.33±0.33 and 11.5±0.29 mm at different concentrations. While the mean zone of inhibition (mm) of different antimicrobial agents at different concentrations for amoxacillin was 24±0.29, 20.67±0.33, 17.67±0.33 and 14.17±0.17mm and for cefquinome was 20.83±0.17, 18±0.29 and 13.5±0.29 mm. no inhibition zones were detected with danofloxacin, sulphaquinoxalline and oxytetracycline Hcl. By macrodilution method, the MIC of rosemary was 0.048mg/ml and the MICs for the aforementioned antimicrobial agents were 0.015, 0.25, 1.0, 8.0 and 16 μg/ml respectively. The synergistic effects were recorded by FIC index between 0.006 and 0.00038 mg/ml of rosemary with 0.125 and 4.0 μg/ml of cefquinome and sulphaquinoxalline respectively.