Myelination of the peripheral nerve occurs predominantly in postnatal period. While several lines of evidence suggested the molecular mechanisms on the myelination, the whole pictures are far from complete understanding. Our previous study showed that myelin formation was positively regulated by hedgehog (Hh) signaling through the primary cilia. Interestingly, the ratio of primary cilia-positive Schwann cells (SCs) gradually increased from the promyelinating phase to the initial stage of myelin sheath formation (~60%), though primary cilia were never observed in myelinated mature SCs (Yoshimura and Takeda, 2012). On this ground, we hypothesized that SCs autonomously determine the sensitive period of Hh signaling for myelin formation. Moreover, we speculated that Hh signaling particularly regulated the early stage of myelination. During the promyelinating phase, SCs showed various profiles of behaviors. The precursors of SCs are derived from neural crest cells, and they developed primary cilia and migrate along axons. Furthermore, SCs stretch their processes and finally ensheath the axons. In this study, we aim to analyze whether or not the effect of Hh signaling is activated in specific stages of promyelinating phase. Although, activation of Hh signaling did not influence the proliferation and migration of SCs, the rate of acetylated- alpha-tubulin positive cells and formation of processes were significantly facilitated. Taken together, these results suggest that primary cilia are formed in immature SCs, and they received the Hh signaling to form the processes (bipolar morphalogy) in promyelinating phase. This temporally well-organized regulation of Hh signaling may modulate the myelination, and therefore, the rate-limiting stage in myelination processes.