Background: Microvascular tissue transfer is a common reconstructive procedure. We designed a bioelectrical impedance assessment (BIA) system for quantitative analysis of tissue status. This study attempts to verify it through the animal model. Methods: The flaps of the rat model were monitored by the BIA system. Results: The BIA variation of the free flap in the rat after the vascular compromise was recorded. The non-vascular ligation limbs of the same rat served as a control group. The bio-impedance in the experimental group was larger than the control group. The bio-impedances of both the thigh/feet flaps in the experimental group were increased over time. In the thigh, the difference in bio-impedance from the control group was first detected at 10 kHz at the 3rd and last at 1 kHz at the 6th h, after vascular compromise. The same finding was observed in the feet. Compared with the control group, the bio-impedance ratio (1 kHz/20 kHz) of the experimental group decreased with time, while their variation tendencies in the thigh and feet were similar. Conclusions: The flap may be monitored by the BIA for vascular status.