Extraneural scarring is one of the factors negatively influencing the result of peripheral nerve surgery. Many organic materials have been used to prevent fibrosis. The effect of aprotinin on peripheral nerve scarring in rats was investigated in this study. Three types of surgical intervention were carried out; namely external neurolysis (I), abrasive injury (II), and anastomosis (III). The coded samples which consisted of pure collagen fibers soaked with aprotinin or phosphate-buffered saline were applied around the left sciatic nerves of rats whereas only sham operations were performed on the right sciatic nerves. Animals were sacrificed after 4 or 6 weeks. Neurological examination, gross evaluation of extraneural fibrosis, and histological study were undertaken. The results have demonstrated that aprotinin is a promising agent in the prevention of extraneural scarring.