Abstract: Objective To observe the effect of course of diabetes mellitus（DM） and controlled blood glucose level on intestinal cleaning degree in elderly diabetic patients before colonscopy. Methods Ninety-nine diabetic patients admitted to our hospital from January 2010 to January 2011 for routine colonscopy were retrospectively analyzed.Their intestine was prepared with the same method and their blood glucose level,duration of DM and intestinal cleaning degree were compared during colonscopy. Results The intestinal preparation was better in patients with their blood glucose controlled than in those with their blood glucose uncontrolled（P=0.002 8）.The longer the duration of DM was,the lower the intestinal cleaning degree was（P=0.049 1）. Conclusion Controlled blood glucose level and duration of DM are correlated with intestinal cleaning degree in elderly diabetic patients when their intestine is prepared with the same method.