Objective To explore the effects of natural hirudin on the survival of dorsal random flap after early pedicle division in rats. Methods Thirty-eight adult Wistar rats, male or female, weighing 220-280 g, were selected and randomly divided into natural hirudin group (experimental group, n=19) and normal saline group (control group, n=19). The dorsal random flap of 9 cm × 3 cm in size was prepared on the back of the rats. Six symmetrical injection points were selected at 2, 4, and 8 cm from the pedicle, 0.5 mL (3 ATU) natural hirudin and equivalent normal saline were injected in experimental group and control group respectively every day to the end of the experiment. After 4 days, the pedicles were cut. The flap was observed, and the ratio of flap survival area was measured at 7 days after pedicle division. At immediately after flap preparation, at 1 day before pedicle division, and at 3 and 7 days after pedicle division, the specimens were harvested for histological staining, immunohistochemical staining, microvessel density (MVD) measurement, and detection of vascular endothelial growth factor (VEGF) mRNA expression by fluorescent quantitative RT-PCR. Results All rats of 2 groups survived to the completion of the experiment. After pedicle division, the flap necrosis area of experimental group was smaller than that of control group; at 7 days, the ratio of flap survival area in experimental group was 85.366% ± 2.872%, and was significantly higher than that in control group (75.252% ± 3.455%) (t=7.117, P=0.000). Histological staining showed that no significant difference was found in the number of capillaries between 2 groups at immediately after flap preparation; at 1 day before pedicle division and at 3 and 7 days after pedicle division, the capillary number of experimental group was significantly more than that of control group. Immunohistochemical staining showed that CD34 positive cells were observed in 2 groups; MVD of experimental group was significantly higher than that of control group at 1 day before pedicle division, and at 3 and 7 days after pedicle division (P lt; 0.05). At 7 days after pedicle division, the VEGF mRNA expression was 7.122 ± 0.503 in experimental group, and was 5.655 ± 1.174 in control group, showing significant difference (t=3.633, P=0.003). Conclusion Natural hirudin can promote the formation of new blood vessels, improve the blood supply of the flap, and increase the survival of random flap after early pedicle division by increasing VEGF expression.