Background: The bowel preparation remains a significant barrier for patients who need to undergo colonoscopy. Inadequate bowel preparations occur in about 10–25% of colonoscopies. So the inadequate nursing intervention leads to inadequate bowel preparation, and serious complications for the patient undergoing colonoscopy. Aim: to examine pre-colonoscopy nursing education and its effect on bowel clearance and colonoscopy complications among patients Undergoing colonoscopy. Design: a quasi-experimental research design was utilized. Setting: Gastrointestinal Endoscopy Unit of Menoufia University Hospital. Sample: Consecutive sample of 60 patients undergoing colonoscopy were assigned randomly into two equal groups, 30 patients for each group: Study group (I): received pre-colonoscopy nursing education along with routine hospital care. Control group (II): received routine hospital care only. Instruments (1): Structured interviewing questionnaire (2): Boston Bowel Preparation Scale (BBPS) (3): Colonoscopy Selected Complications Assessment Sheet. Results: The findings revealed that there were highly significant differences were existed between study and control groups regarding their degree of bowel clearance (P< 0.001) in addition to there were significant differences between study and control groups regarding incidence of problems and complications of abdominal pain and abdominal distention. Conclusions: Pre colonoscopy nursing education significantly improves the quality of bowel clearance among study group subjects compared to control group subjects. Moreover; pre colonoscopy nursing education had a positive effect on reducing incidence of patient's problems and complications among study group subjects compared to control group subjects. Recommendations: designing pre-colonoscopy nursing education programs to help the patients in the preparation of colon for colonoscopy to reduce incidence of problems and complications in addition to; training program for nurses to improve their skills patients' education regarding colonoscopy preparation and the importance for seeking rapid medical advice.