Background. Postoperative peritoneal adhesions (PPA) are a serious problem for abdominal surgery. An effective remedy has not been found yet. New formulation of glycerol and sodium pentaborate may be able to solve the problem. Method. Female Wistar albino rats were randomly assigned into four equal groups. The adhesion model was created on the caecum anterior wall and covered with 2 ml 0.9% NaCl, 3% glycerol, 3% sodium pentaborate, and 3% glycerol plus 3% sodium pentaborate solutions in the groups, respectively. Two weeks later, the rats were sacrificed. PPA were graded macroscopically and microscopically. Results. Total adhesion scores of the 3% glycerol + 3% sodium pentaborate group were statistically different from the other groups for macroscopic and also microscopic evaluations (p<0.001). Conclusion. 3% glycerol plus 3% sodium pentaborate as a new formulation has preventive effects on PPA with a synergistic mechanism.