【Abstract】Objective To analyze the clinical characteristics, diagnosis and safety of preschool children undergoing colonoscopy in Chengdu.Methods Clinical data of 433 preschoolers aged 06 years underwent colonoscopy in Chengdu Women and Children's Central Hospital from January 2018 to August 2020 were retrospectively analyzed. There were 265 males and 168 females, with a maletofemale ratio of 158〖DK〗∶1, which were divided into two groups, including 227 cases aged 03 years old and 206 cases aged 36 years old.Results 440 times of colonoscopy were performed in 433 children, 382 times of colonoscopy were inserted into the cecum, and the total colon examination was completed. The main reasons included hematochezia in 281 cases (649%), diarrhea of unknown origin in 114 cases (263%), abdominal pain in 13 cases (30%), anus or intestinal mass in 12 cases (28%), constipation in 5 cases (11%), postoperative intestinal surgery in 3 cases (28%), and lower gastrointestinal foreign body in 2 cases (0.5%). The causes of hematochezia, abdominal pain, constipation, diarrhea, anus or intestinal mass were significantly different between the 03 years old and the 46 years old group.Full set of 396 (915%) cases were detected lesions, with 158 cases of chronic colitis (365%), colorectal polyps in 127 cases (293%), 62 cases of allergic colitis (143%), inflammatory bowel disease in 5 cases (11%), vascular abnormalities in 5 cases (11%), and HenochSchnlein purpura, intestinal tuberculosis, hemorrhoids, anal fistula, foreign body of gastrointestinal tract, and so on a total of 39 cases (9%). There were significant differences between the two groups in chronic colitis, allergic colitis, polyps and abnormal vascular diseases. Adverse events were observed in 45 (104%) patients, and most of them are transient and mild, 9 (21%) patients with abdominal pain, 22(25%) patients with transient fever, 14 (23%) patients with bleeding, and no perforation.Conclusion Painless colonoscopy in children is safe and plays an important role in the diagnosis of the chronic diarrhea, hematochezia and other diseases. The diseases detected by colonoscopy in preschool children have their specific disease spectrum, and the proportion of diseases is also different between 03 years old and 36 years old group.