Abstract The frictional behaviors of prepreg-prepreg and prepreg-tool play the most important role in hot diaphragm forming and greatly influence the quality of the final product. A new set-up was developed to characterize the frictional behaviors for unidirectional carbon fiber/epoxy prepreg. The effects of temperature, normal force, pulling rate, and relative fiber angles on the frictional behaviors of the prepreg-prepreg and prepreg-tool interface have been investigated. Results of these tests are presented and observations are noted. The results show that the frictional resistance increases with increase in the normal force and the pulling rate, and its variation with the temperature is complicated. The frictional resistance is higher at 90° fiber orientation to the pulling direction than that at 45° and 0°.