Fibroblast growth factor 9 (FGF9) is crucial for the growth and development of hair follicles (HFs); however, its role in sheep wool growth is unknown. Here, we clarified the role ofFGF9in HF growth in the small-tailed Han sheep by quantifyingFGF9expression in skin tissue sections collected at different periods. Moreover, we evaluated the effects ofFGF9protein supplementation on hair shaft growth in vitro andFGF9knockdown on cultured dermal papilla cells (DPCs). The relationship betweenFGF9and the Wnt/β-catenin signaling pathway was examined, and the underlying mechanisms ofFGF9-mediated DPC proliferation were investigated. The results show thatFGF9expression varies throughout the HF cycle and participates in wool growth. The proliferation rate and cell cycle ofFGF9-treated DPCs substantially increase compared to that of the control group, and the mRNA and protein expression ofCTNNB1, a Wnt/β-catenin signaling pathway marker gene, is considerably lower than that in the control group. The opposite occurs inFGF9-knockdown DPCs. Moreover, other signaling pathways are enriched in theFGF9-treated group. In conclusion,FGF9accelerates the proliferation and cell cycle of DPCs and may regulate HF growth and development through the Wnt/β-catenin signaling pathway.