PURPOSE: This study was done to evaluate the clinical and pathologic aspects of allergic colitis. METHODS: This study evaluated 19 infants who presented with fresh blood mixed stools. Limited colonoscopy and biopsy were performed. Among the 19 infants, 13 infants were diagnosed as allergic colitis by histological findings. We analyzed the clinical and histological characteristics of 13 infants. RESULTS: Male and female were 8 and 5 respectively. The mean age of the infants was 3 months (4 days to 12 months). Major symptoms were rectal bleeding (13), mucoid stool (6), diarrhea (5), vomiting (2). Feedings before diagnosis were breast milk (3), formula milk (4), formula and breast milk (5), and weaning diet (1). In labortory data, anemia (2) and eosinophilia (12) were found in some infants. Endoscopic findings were focal erythema (7), nodularity (1), erythema and nodularity (4), hemorrhage (1). Histopathologic finding was eosinophilic infiltration in lamina propria with preserved mucosal architecture in all. In addition, cryptitis (13), lymphoid follicular hyperplasia (7), crypt abscess (1) were also observed. All the infants improved with cessation of rectal bleeding and diarrhea within three days after dietary change. CONCLUSION: Allergic colitis should be considered as one of the major cause of rectal bleeding in healthy appearing infants. Limited colonoscopy and biopsy should be considered in establishing a definitive diagnosis.