We performed a retrospective study using 161 colorectal surgical patients to explore the additional medical costs due to postoperative infections. Patients were divided into two groups based on antimicrobial drug use duration: the control group included 112 patients with standard antimicrobial prophylaxis use, and the case group included 49 patients with additional antimicrobial drug use （indicating postoperative infection）. The case group had additional medical costs of US$7,993 （95% CI: 5,481-10,506）and hospital stay of 24.8 days （95% CI: 17.5-32.2）. Factors significantly associated with postoperative infections were preoperative physical status scores of 3 or higher （OR: 3.447, 95%CI: 1.127-10.546）, preoperative ileus （OR 6.618, 95%CI: 2.491-17.579）, hypertension （OR: 2.140, 95%CI: 1.082-4.232）, contaminated surgery （OR: 11.784, 95%CI: 3.151-44.066）, open surgery （OR: 2.111, 95%CI: 1.065-4.187）, and operative duration exceeding 400 minutes （OR: 2.465, 95%CI: 1.111- 5.471）. These findings suggest that hospital administrators should take appropriate measures to prevent postoperative infections in surgical inpatients.