Background: Wnt/モ-catenin signaling regulates hair growth and the structure of hair shaft. On the other hand, reactive oxygen species (ROS) play a role as intracellular messengers and over-generated and uncontrolled ROS can damage many cellular components. H2O2, especially, causes inhibition of Wnt/モ-catenin signaling. Objectives: Current study investigates the mechanism of effect of ROS on Wnt signaling in terms of hair growth. Methods: We measured the length of the hair follicle in vitro organ culture. Cell viability of cultured rat dermal papilla cells (DPCs) were evaluated by MTT assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide]. We measured the expression of GSK3モ, モ -catenin and CyclinD1 by Western blot in rat DPCs after H2O2 treatment. We measured gene level of モ-catenin by using real time PCR. Finally, we measured the expression of モ-catenin by Western blot in human DPCs after H2O2 treatment. Results: The study found that H2O2 inhibited growth of hair follicle and dermal papilla cells. H2O2 also had negative influence on proteins affecting Wnt/モ-catenin signaling. Under H2O2 treatment condition, GSK3モ has activated the level of expression of モ-catenin and CyclinD1 has decreased. LiC1, however, inhibits the effect of H2O2, and we obtained similar effect of H2O2 on human DPCs. Conclusion: H2O2 inhibit expression of proteins involving Wnt/モ-catenin signal which is essential to hair growth. From the results, we expect H2O2 can suppress hair growth.