Medicinal leech therapy is commonly used to treat venous congestion by local application to skin flaps, which are frequently employed in re-construction surgery. In the present study, we investigated the effect of natural hirudin, which was applied locally to treat the venous congestion, in random skin flaps in a Guangxi Bama miniature pig model. The congestive random skin flaps were divided into 3 groups: Group A (control group that was locally applied with saline), Group B (locally applied with 20ATU natural hirudin per each flap), Group C (locally applied with 40ATU natural hirudin per each flap). The microcirculatory changes were observed by measuring myeloperoxidase (MPO), malondialdehyde (MDA) and superoxide dismutase (SOD). The level of MPO, MDA and SOD activities in the tissue in hirudin-treated groups was significantly different compared with control group (P < 0.05), but there was no significant difference between group B and group C. At 12 days, as compared to the control group, flap survival rate in hirudin-treated groups was significantly different (P < 0.05), but there was no significant difference between the groups receiving two different doses of hirudin. Natural hirudin can improve microcirculation by inhibiting oxygen free radical damage and also improve flap survival time.