A total of 100 strains of Staphylococcus. aureus were isolated from patients in the Affiliated Hospital of Inner Mongolia Medical University ［methicillin resistant Staphylococcus aureus（MRSA） and methicillin sensitive Staphylococcus aureus（MSSA）］，and the bacterial identification and antibiotic susceptibility test to 12 kinds of antibiotics were performed.The gene typing was performed by adopting accessory gene regulator （agr） typing method.The pvlgene and 31 virulence genes were analyzed by PCR method. The biofilm-forming ability was assessed using the crystal violet staining method.

Among 100 pvl negative Staphylococcus aureus clinical isolates， 38 isolates were MSSA， while 62 isolates were MRSA. The Staphylococcus aureus isolates were all sensitive to vancomycin， linezolid and quinupristin/dalfopristin， but the resistance rates of MRSA to the other antimicrobials were higher than those of MSSA isolates. The agr genotyping results showed that agr-Ⅰ to agr-Ⅳ types were all found among the Staphylococus aureus isolates， and agr-Ⅰ type was found to be the dominant type， accounting for 79.0%， followed by agr-Ⅱ type （16.0%）. The carriage rate of agr-Ⅱ type among MSSA isolates was significantly higher than that of MRSA isolates （81.3% vs 19.7%，P<0.05）. Moreover， the carriage rate of agr-Ⅰ type among MRSA isolates was significantly higher than that of MSSA isolates （72.2% vs 27.8%，P<0.05）. Among 32 virulence genes detected in this study， the positive rates of hla and hld genes were all 100%，while no isolate carried edin， etb and pvl gene. The carrige rates of sdrE， sea， seb， seH， tsst， lukDE， lukM， hlb， mpHLG2-1 among MRSA isolated were higher than those of MSSA isolates， when carrige rates of sea and seh（56.5% and 79.0%） were higher than those of MSSA （7.9 and 60.5%）（P<0.05 or P<0.01）； the carriage rates of the other 18 virulence related genes of MRSA were all lower than those of MSSA isolates， and the carriage rates of mpHLG， seo， sed and sej among MRSA isolates were significantly lower than those of MSSA isolates （P<0.05 or P<0.01）； 23.7% （9/38） MSSA isolates carried at least 15 virulence genes， which was significantly higher that of MRSA isolates［14.5%（9/62）］. Furthermore， the biofilm producing isolates among MSSA and MRSA isolates accounted for 100%（38/38） and 85.5%（53/62） （P<0.05），respectively.

Among 100 pvl-negative Staphylococcus aureus clinical isolates， agr-Ⅰ type is the most predominant. The MRSA isolates show higher prevalence of resistance to multiple antimicrobials， while the carrying rates of virulence genes among MSSA isolates are higher than those of MRSA isolates. The biofilm forming ability of MSSA isolates is higher than that of MRSA isolates.