Background: Female-pattern hair loss (FPHL) is a common hair loss disorder in women. The various treatments include topical minoxidil and 17α-estradiol, as well as oral anti-androgens. However, the clinical efficacy of 5α -reductase inhibitors remains controversial. Objective: We evaluated the clinical utility of dutasteride in FPHL patients and how dutasteride promotes hair growth. Methods: We evaluated hair follicle density and thickness before and after oral dutasteride treatment in 24 patients with FPHL. We measured β-catenin activity in primary cultures of human dermal papilla cells (DPCs) using the TOP Flash reporter assay and Western blotting. The expression levels of genes promoting hair growth were quantitatively assessed using quantitative polymerase chain reaction (Q-PCR). Results: The mean vertex hair density increased significantly from 67±14 to 76±13/cm² (p=0.001) and the mean occipital hair density increased from 89±11 to 94±13/cm² (p=0.012) after dutasteride treatment. However, the mean hair thickness did not increase. When DPCs were treated with dutasteride, TOP Flash activity increased in a dose-dependent manner, and the protein level of non-phosphorylated (active) β-catenin also increased. The mRNA level of vascular endothelial growth factor increased, but the mRNA levels of the keratinocyte growth factor, insulin growth factor-1, and Noggin were not affected by dutasteride. Conclusion: This study shows a novel mechanism of dutasteride in promoting hair growth and provides support for the possible clinical application of 5α-reductase inhibitors for the treatment of FPHL. (Korean J Dermatol 2020;58(4):231∼238)