Objective To study the clinical manifestations and gastroscopic characteristics of upper gastrointestinal ulcer in children. Methods A retrospective analysis was performed for the children who underwent gastroscopy and were found to have upper gastrointestinal ulcer for the first time at the Endoscopy Center of Shengjing Hospital, China Medical University, from January 2011 to May 2021. According to the cause of the disease, they were divided into primary ulcer group (primary group; n=148) and secondary ulcer group (secondary group; n=25). The clinical data were compared between the two groups. Results A total of 173 children with upper gastrointestinal ulcer were enrolled, with a male/female ratio of 3.9:1. Compared with girls, boys had significantly higher proportions of duodenal ulcer and primary ulcer (P<0.05). Compared with the children aged below 6 years, the children aged 6-14 years had higher proportions of duodenal ulcer and primary ulcer and lower proportions of giant ulcer and multiple ulcers. Of the 148 children in the primary group, 95 (64.2%) had Helicobacter pylori infection. Abdominal pain was the most common clinical symptom and was observed in 101 children (68.2%). Duodenal ulcer was common and was observed in 115 children (77.7%), followed by gastric ulcer in 25 children (16.9%) and esophageal ulcer in 7 children (4.7%). Multiple ulcers were observed in 32 children (21.6%). Seventy children (47.3%) experienced complications, among which bleeding was the most common complication and was observed in 63 children (43.6%). Of the 25 children in the secondary group, abdominal pain was the most common clinical symptom and was observed in 9 children (36.0%), with a significantly lower incidence rate than the primary group (P<0.05); foreign body in the digestive tract was the most common cause of ulcer and was observed in 17 children (68%), followed by abdominal Henoch-Sch?nlein purpura in 5 children (20.0%) and Crohn's disease in 3 children (12.0%). The secondary group had a significantly higher proportion of multiple ulcer or giant ulcer than the primary group (P<0.05). Conclusions Upper gastrointestinal ulcer is more common in boys than girls, and duodenal ulcer and primary ulcer are more common in boys. Children aged 6-14 years often have duodenal ulcer and primary ulcer, and giant ulcer and multiple ulcers are relatively uncommon. Primary ulcer in children has a variety of clinical manifestations, mainly abdominal pain, and duodenal ulcer is relatively common, with bleeding as the main complication. The clinical symptoms and endoscopic manifestations of secondary ulcer are closely associated with the primary causes, and it is more likely to induce huge ulcers and multiple ulcers.