Sargassum fusiforme has traditionally been widely consumed in Asia as a food, and it has gained much attention due to its high nutritional, pharmaceutical, and industrial value. This study aimed to examine the promotional effects of ethanol extract (ET) and fraction obtained from ethyl acetate (FR) of S. fusiforme on hair growth in C57BL/6 mice and HaCaT cells. Five-week-old mice were used to compare hair regrowth during application of ET and FR for 21 days. Hair regrowth was evaluated by macroscopic observation and verified by hematoxylin-eosin tissue staining. Levels of mRNA expression of factors relevant to the hair growth cycle such as keratinocyte growth factor (KGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta1 (TGF-beta1) were examined by quantitative polymerase chain reaction (qPCR). Our results showed that ET and FR successfully promoted hair regrowth in shaved C57BL/6 mice at a dose >20 mg/kg. Moreover, ET and FR were effective in stimulating expression of KGF and VEGF mRNAs in a dose-dependent manner, whereas TGF-beta1 was not activated. These results indicate that ET and FR of S. fusiforme effectively promoted hair growth and gene expression relevant to hair growth cycles in both in vitro and in vivo models.