To investigate biofilm formation on the surface of silica gel by breast surgery clinical specimens of Staphylococcus epidermidis and to analyze the relationship between biofilm formation and icaA, icaD, and accumulation-associated protein (aap) gene.Between December 2011 and January 2013, 44 strains of Staphylococcus epidermidis were isolated from the clinical specimens of the female patients who had no symptom of infection. The icaA, icaD, and aap genes were detected by PCR and 4 genotypic groups were divided: icaA+ icaD+/aap+ group (group A), icaA+ icaD+/aap- group (group B), icaA- icaD-/aap+ group (group C), and icaAicaD/aap group (group D). Biofilms mass was semi-quantified by semi-quantitative adherence assay after 8, 12, 24, 30, and 36 hours of incubation. The thickness of biofilms was measured by confocal laser scanning microscope (CLSM) at 12 and 24 hours after incubation. The ultrastructure of biofilms was observed by scanning electron microscope (SEM) at 24 hours after incubation.PCR test showed that 13 strains were icaA+ icaD+/ aap+ (group A), 12 strains were icaA+ icaD+/aap- (group B), 16 strains were icaA- icaD-/aap+ (group C), and 3 strains were icaA- icaD-/aap- (group D). In 29 strains which had bacterial biofilm formation (65.9%), there were 13 strains in group A, 7 strains in group B, 9 strains in group C, and 0 in group D. The result of semi-quantitative adherence assay showed no significant difference in the absorbance (A) values among 4 groups at 8 hours (P > 0.05). The A values of groups A, B, and C were significantly higher than that of group D at 12-36 hours, and group A was significantly higher than groups B and C (P 0.05). The results of CLSM showed that the thickness of biofilm in groups A, B, and C was significantly larger than that in group D at 12 and 24 hours after incubation (P 0.05). The result of SEM showed that the mature biofilm could be observed on the surface of silica gel in groups A, B, and C, and the ultrastructure of biofilms in group A were the most abundant and extensive among 3 groups. The ultrastructure of biofilm in group B was similar to that in group C. No obvious biofilms formed in group D.icaA, icaD, and aap genes all play key roles in the process for biofilm formation of Staphylococcus epidermidis. Futhermore, aap gene enhance the ability of biofilm-forming when aap and ica genes coexist, so the biofilm-forming ability of icaA+ icaD+/aap+ is strongest.