Abstract： Objective To determine whether the novel surface-anchored protein SasX promotes aggregation of S.aureus and adherence of S.aureus to human nasal epithelial cells.Methods MRSA ST-239 HS770 sasX gene mutant ( HS770 △sasX) and complement [ HS770 △sasX (pRBsasX) ] were gotten by gene knock-out and complement methods.The aggregation ability of S.aureus was observed through microscope.By adherence assay which was used for detection of the adherence ability of wild type and mutant to human nasal epithelial cells and blocking experiments which detected the ability of the purified recombinant SasX protein in blocking the adherence of S.aureus to human nasal epithelial cells,we investigated the influence SasX on colonization of S.aureus.Results Compared to wild type,HS770△sasX showed a reduction in cell aggregation,while the complement had no difference with wild type in aggregation. HS770 △sasX showed a significant reduction of adherence to human nasal epithelial cells compared to wild type ( P＜0.01 ),and the complement showed a very clear increasement of adherence to human nasal epithelial cells compared to wild type(P＜0.01 ).Preincubation of nasal epithelial cells with the purified recombinant SasX protein inhibited S.aureus binding significantly.Conclusion SasX had an influence in aggregation of S.aureus and its adherence to human nasal epithelial cells.By acquiring sasX,S.aureus colonized more easily to the susceptible sites of the host,and thus caused infection.