Post operative adhesion is the most common cause of small bowel obstruction, infertility and technical problem in later surgical procedure. According to some results on animals or human, non-closure parietal peritoneum have performed less adhesion. Since there are considerable controversies over closure or non-closure parietal peritoneum on amount of adhesion after cesarean section. 300 pregnant women were included in this study. The parietal peritoneum in 148 patients was closed and in 152 patients left opened. In their next cesarean section, which was at least 31- 34 months later, the amount of adhesion and hernia were evaluated and recorded. The results showed that there were no statistically significant difference between the two groups over age, weight, parity and pelvic infection but there was a significant difference between the interval of two successive surgeries and type of surgeries: elective or emergency (p<0.05). The adhesion evaluation of abdominal wall, fascia, peritoneum, omentum, bowel and bladder in non-closure and closure peritoneum patients were 38.5%- 98%, 8.1%- 53.3%, 18.9%- 7.4%, 72.4%- 2.7%, 18.4%- 31.1% and 94.1% respectively. The reaults showed a significant difference in the amount of adhesion between two groups (p<0.001). It was much lower in the non-closure group. The comparision of total score of adhesion with age, weight and parity in two groups were not statistically significant. Althouh the results of our study showed the open peritoneum is better than closed parietal peritoneum but we can not generalize for all abdominal surgery. Therefore more reseach would be necessary.