Static Sciatic Index (SSI), a conventional footprint analysis in animal models, is widely used for the evaluation of motor function in sciatic nerve-injured rats. However, the sciatic nerve is divided into two branches, the tibial nerve and the common peroneal nerve. Thus, we first examined which nerve component had more effect on motor function assessed by SSI by the nerve-lesioning experiments. Functional assessments by SSI were performed after resection of the tibial nerve or the common peroneal nerve in adult rats. As a result, it was revealed that motor dysfunction of the common peroneal nerve-resected rats was more severe than that of the tibial nerve-resected rats. In the next, we investigated effect of undamaged residual axons on motor function in the nerve-crushed rats. For this purpose, adult rats received various degrees of crush injuries to the common peroneal nerve as follows. The left common peroneal nerve was crushed with a brain aneurysm clip for 1, 2, 3, 4, 5, and 10 s or a disposable micro vascular clip for 1, 20, 60, 80, 90, 100, 110, 120, and 180 s. The assessments of SSI and slope walking ability were performed after various nerve-crush injuries, and the tibialis anterior muscle was removed and cut for frozen sections. The numbers of residual undamaged axons were measured by immunohistochemically visualized βIII-tubulin, an axonal marker. The numbers of histochemically visualized α-bungarotoxin, an acetylcholine receptor antagonist, were also measured in the same sections. The results showed that motor function assessed by SSI and slope walking ability was correlated with the ratios of residual axons to acetylcholine receptors, and that normal motor function was well preserved if residual axons accounted for more than 40% of the control value.