The aims of this study were to determined whether excitability of the $alpha$-motor neuron is modulated by stretching and this changes were associated with flexibility of the muscle. In this study, $alpha$-motor neuron excitability was measured by using the Hmax/Mmax ratio of the gastrocnemius H-reflex, and muscle flexibility was measured with the range of motion of the ankle dorsiflexion. The gastrocnemii of 10 healthy volunteers were stretched for 4 minutes(2 minutes stretching, 1 minute rest, and 2 minutes stretching) in each session by manual force. The Hmax/Mmax ratio of the H-reflex, as well as the range of motion of the ankle dosiflexion was measured through four different conditions: before stretching, as soon as after $1^{st}$ stretching, as soon as after $2^{nd}$ stretching and at 48 hours after $2^{nd}$ stretching. Excitability of the $alpha$-motor neuron was decreased significantly after $1^{st}$ and $2^{nd}$ stretching(p<0.05). Furthermore, the range of the dorsiflexion was increased significantly after $1^{st}$ and $2^{nd}$ stretching(p<0.05). However, the excitability of the $alpha$-motor neuron and range of the dorsiflexion at 48 hours after $2^{nd}$ stretching were not different from those of before stretching. These results suggest that reduced $alpha$-motor neuron excitability of the gastrocnemius and increased flexibility of the ankle dorsiflexion would be followed by activation of the type III mechanoreceptor which around the ankle joint and the Golgi tendon organ in the gastrocnemius.