We assessed the clinical impact of the systemic use of antibiotics on postoperative infection in colorectal surgery. Perioperative administration prevents postoperative infection: a statement which is based on the results of five randomized controlled trials performed in the 1970s and 1980s. Our study design was a randomized controlled trial. We created two groups, one using the systemic antibiotic cefotiam (CTM), and the other using no antibiotic as the control. The primary end point was the overall postoperative infection rate. There were 100 patients assigned to this study. The patients were divided into two groups; the control group consisted of 51 cases and the CTM group had 49 cases. The backgrounds of the patients in the two groups were not significantly different. The overall postoperative infection rate was 28/51 (54.9%) in the control group and 25/49 (51.0%) in the CTM group. The surgical site infection (SSIs) (superficial, deep, and space/organ ) were 23/51 (45.1%) in the control group and 20/49 (40.8%) in the CTM group. No significant difference was observed between the CTM group and the control group regarding postoperative infection after elective colorectal surgery.