Objective To study the bowel cleanliness and safety in the elderly with different ways of bowel preparation before colonoscopy. Methods A total of 120 patients were divided randomizely into 4 groups (n=30). For bowel preparation, patients in the first group(A group) received polyethylene glycol electrolytes (PEG); the second group(B group) received PEG and 500ml enteral nutrient; the third group(C group) took magnesium sulfate (MgSO4); the forth group(D group) were given MgSO4 and 500 ml enteral nutrient. Bowel preparation quality of every patient was monitored, the change of body mass (BM), blood pressure (BP), fasting blood glucose (FBG), side effects on heart or brain were collected and analyzed. Results The total effective rate of bowel preparation was more than 80%, the intestinal cleanliness efficiency of each group was similar (P＞0.05); The patients in group B and group D who took enteral nutrient got less change in BM, FBG, BP, heart rate after bowel preparation than those in group A and group C (P＜0.05). No hypoglycemia, shock, dizziness, angina, or vomiting occurred in group B and D with the addition administration of nutrient solution, no patient required intravenous fluids administration, which was significantly better than the cases in group A and C. Conclusion Taking enteral nutrient for bowel preparation before colonoscopy can reduce patient’s side effect and keep the bowel preparation quality, it is a safe way for bowel preparation in the elderly patients.