Objective To assess visceral hypersensitivity and constancy of visceral hypersensitivity models of irritable bowel syndrome (IBS) in rats. Methods Two-day-old Sprague-Dawley rat pups were randomly divided into the neonatal maternal separation group (group A), the unpredictable neonatal maternal separation group (group B), and the control group ( group C). After successful modeling, the rats’ general conditions and stools were observed, and their visceral hypersensitivity and constancy were determined via the abdominal wall withdrawal reflex and visceral pain threshold. After testing, the rats’ colonic tissue was taken for pathological examination. Results Body weight and colonic pathological examinations did not differ between the groups (P> 0. 05). Compared with groups A and C, rats in group B had increased stools and stool water content. Compared with groups B and C, the abdominal withdrawal reflex(AWR) threshold was highest in the group A rats and peaked at 9 weeks of age. The visceral pain threshold did not differ between groups A and B but was lower in both groups compared with that of group C (P > 0. 05). Conclusions Both the neonatal maternal separation and the unpredictable neonatal maternal separation models simulated the IBS visceral hypersensitivity model. The unpredictable neonatal maternal separation model better simulated a diarrheal IBS model. The visceral hypersensitivity model was time-limited, and the optimal experimental time was within 9 weeks of age.