(Background) The prevalence of surveillance of surgical site infection(SSI)have been playing important role in the prevention for the postoperative infection. However, intraoperative bacterial contamination (IBC) which can be a major cause for SSI has not been well investigated. (Aim) The aim of study is to investigate whether ingenuity of surgical procedure could have an effect on decrement to IBC/SSI rate. (Methods) The subjects were 50 patients who underwent elective colorectal surgery (anterior resection (AR)/34, Hartmann’s-Mile’s operation (HM)/16) from November 2004 to June 2007. Of these, adoral colonic transection in early period during surgery (early transection: E-Tx) was performed in 30 patients (AR: 21, HM: 9) and late colonic transection, which colonic continuity was not cut off until anastomosis or stomal construction (late transection: L-Tx) was in 20 patients (AR: 13/HM: 7). Three samples as of 1) lrrigation fluid before abdominal closure (CLOS), 2) remained cutting suture ligated for peritoneal closure (SUTURE), and 3) subcutaneous swab of surgical wound (SUBCUT) were obtained intraoperatively and examined for the bacterial identification. Results The overall SSI rate was 26% (AR: 4/HM: 9) and all SSI occurred superficially. Eleven out of 13 SSI patients had extremely high IBC rate of 85%, as well as IBC patients had high SSI rate at 72%. Bacterial detection was highest in the CLOS (26%), and SUBCUT (26%), and followed by SUTURE (12%). SSI rate of L-Tx group was significantly lower than that of E-Tx group (10% vs. 36.7%, p<0.05). Comparison of IBC rate between those 2 groups was also significant (E-Tx: 47%/ L-Tx: 20%, p<0.05). Conclusion Intraoperative contamination was considered as the one of important factor for SSI. Both IBC and SSI rate can be reduced by the shortening of transected colonic time from which might contaminated by bacteria. Therefore thorough control of IBC should reconsider as the priority for SSI prevention than other remedy.