Objective To find the difference between the collagenase activity and tissue inhibitor of metalloproteinase-1 (TIMP-1) expression level in normal urethral tissue and in urethral scar tissue, and to study the effect of collagenase activity and TIMP-1 expression level on the degradation of urethral scar. Methods The urethral tissues were derived from 10 human surgical specimens of urethral stricture scar and 10 human normal urethral specimens from patients with brain death. The collagenase activity was detected by ELISA assay, and the TIMP-1 mRNA level by RT-PCR. Results The collagenase activity of urethral scar tissue was (15.32±2.29) U and lower than that of normal urethral tissue (24.67±6.78) U, there was significant difference between them (P lt; 0.01). The TIMP-1 expression level of urethral scar tissue was higher than that of normal urethral tissue, there was significant difference between them (P lt; 0.05). Conclusion The high level of TIMP-1 expression and the low collagenase activity in urethral scar tissue may inhibit the degradation of urethral scar, and may be one of important causes of the scar tissue hyperplasia.