Although it is well established that women are more likely to sustain certain connective tissue injuries than men during physical activities, this difference between males and females is not clear. Gelatinases degrade components of tendon tissue. Thus, in this research, the effects of gender on serum gelatinases (MMP-2 and MMP-9) at rest and in response to acute endurance exercise were investigated. 15 healthy and active men and 15 healthy and active women participated in this study. Subjects exercised for one hour at 70% of VO2max on an ergometer 72 hours after VO2max had been determined. Two mls of antecubital vein blood was collected before, immediately after and 2 hours after the exercise. Serum MMP-2 and MMP-9 were measured by ELISA method. ANOVA with repeated measures and one-way ANOVA were used to analyze the data (P?0.05). The results showed that MMP-2 and MMP-9 at rest in men and women were not different. MMP-2 decreased in both groups immediately after the exercise while this decrease in women was not significant. Serum MMP-2 did not change in both groups in response to the exercise. There was no difference in the changes of MMP-2 and MMP-9 in response to the exercise between the two groups. According to the results of this study, the gelatinases at rest and in responses to acute exercise is not an effective factor in more vulnerability of tendon tissues in women in response to the exercise. Presumably, other hormonal and structural factors of women’s tendon are responsible for more injuries