Hair growth is regulated by the interaction between dermal papilla cells (DPC) and other cells inside the hair follicle. Here, we show the effect and action mechanism of mackerel-derived fermented fish oil (FFO) extract and its component docosahexaenoic acid (DHA) in the control of hair growth. The hair growth effect of FFO extract was evaluated by the culture method of vibrissa follicles and in vivo dotmatrix planimetry method. FFO extract increased the length of hair-fibers and enabled stimulated initiation into the anagen phase of the hair cycle. As expected, FFO extract significantly increased DPC proliferation. FFO extract induced the progression of the cell cycle and the activation of extracellular signal-regulated kinase (ERK), p38 and Akt. FFO extract induced nuclear translocation of β-catenin, a stimulator of anagen phase, through an increase of phospho-glycogen synthase kinase3β (GSK3β) level. Since various prostaglandins are known to promote hair growth in humans and mice, we examined the effect of DHA, a main omega-3 fatty acid of FFO, on DPC proliferation. DHA not only increased DPC proliferation but also upregulated levels of cell cycle-associated proteins such as cyclin D1 and cdc2 p34. These results show that FFO extract and DHA promote hair growth through the anagen-activating pathways in DPC.