Surgical site infection (SSI) is a major postoperative complication after abdominal surgery especially in colorectal field, which significantly increases length of stay (LOS), readmission incidence and expense. Therefore, identification of the effective method to reduce SSI incidence is critically important. Combination of oral antibiotics and mechanical bowel preparation was reported with lower SSIs and LOS in some retrospecitve data analysis, however a prospective randmized controlled trial was absent. Herein, the current randomized controlled trial comparing MBP+OA with MBP alone in postoperative complications in order to guide clinical practise was conducted.

Surgical site infection (SSI) is a major postoperative complication after abdominal surgery especially in colorectal field, which significantly increases length of stay (LOS), readmission incidence and expense. Therefore, identification of the effective method to reduce SSI incidence is critically important. Colonic bacterial flora is the major cause of SSIs after elective colorectal procedures. For more than century, preoperative mechanical bowel preparation (MBP) has been utilized as it could theoretically decrease bacterial load within the surgical field, thus reduce risk of SSIs. Later afterwards with widely application of antibiotics, combination of oral antibiotics (OA) and MBP was conducted by surgeons to further decrease rates of SSIs. But SSIs still occurs despite of forehead mentioned methods, the best bowel preparation mode remains controversial. Since 2005, several RCTs and meta-analysises demonstrated MBP alone was not associated with reduced SSIs compared with no bowel preparation, while postoperative ileus, anastomotic leakage and other complications incidence increased paradoxically. Nevertheless, function of preoperative oral antibiotics remains debated. Recently, combination of oral antibiotics and MBP has been evaluated in several retrospective studies and demonstrated a significant decrease in the rate of SSIs. However, bias existence in these trials may affect result as information was exacted from national database without detailed matching. Herein, current randomized controlled trial comparing MBP+OA with MBP alone in postoperative complications in order to guide clinical practise was conducted.

Inclusion Criteria:

• Older than 18 years old，
• Undergoing laparoscopic colorectal surgery due to malignancy.

Exclusion Criteria:

• No elective surgery
• Intra-abdominal infection
• Combination of other infectious surgery such as appendectomy, cholecystomy
• Sever comobidity such as uncontrolled hypertention and diabetes mellitus
• Peritoneal implantation and matastasis
• Radiotherapy history.
• Colorectal surgery due to benign lesions
• Allergic to antibiotics or PEG
• Preoperative dermatosis may interfere wound healing
• Long time application of corticosteroid
• Autoimmune disease may affect wound healing
• Patients refuse to enroll

No masking is to conducted in the current study.