ObjectiveTo investigate the occurrence and susceptibility factors of surgical site infection(SSI) in patients undergoing oralmaxillofacial surgery with microvascular freeflap reconstruction.MethodsFrom December 2010 to September 2011, a prospective survey was performed to monitor the susceptibility factors for SSI in 257 patients undergoing oralmaxillofacial surgery with microvascular freeflap reconstruction, the surveyed contents  included age, sex, the nature of disease, American Society of Anesthesiologists(ASA) score, white blood cell, hematoglobin, length of hospital stay, length of surgery, types of incision, intraoperative blood loss and so on. Patients were followed up after  1, 3 and 6 months of operation,the occurrence of SSI at different stages were surveyed.ResultsOf 257 patients, 46 (17.90%) developed SSI, and all were deep wound infection,19 (41.30%) of whom had SSI during hospitalization period, and 27 (58.70%) were found through postdischarge followup investigation. Infection occurred 5-34 days  after  operation, the median time was 11 day. Monitoring of susceptibility factors showed that,except  the duration of intraoperative antimicrobial use  (≤110 min) was statistically significant (P<0.05), other factors were not statistically significant (P>0.05).ConclusionIncidence of SSI is high  in oralmaxillofacial surgery with microvascular freeflap reconstruction, and mostly  occur in patients after discharging from  hospital. In order to reduce SSI effectively, clinical attention should be paid, postoperative followup should be intensified, intervention in susceptibility factors should be performed, and antimicrobial agents should be used rationally.