The effects of $Cuscuta$ $japonica$ BuOH fraction (CJBF) on the proliferation of human hair dermal papilla cells (HHDPCs) and on the stimulation of hair growth in a cyclophosphamide (CYP)-induced alopecia model C57BL/6 mouse were studied. In cell-based MTT assay, the proliferation rates were increased 25% in CJBF treated group of CYP-treated HHDPCs. Gene expression-based RT-PCR study was conducted to find the mechanism. The ratio of $Bcl-2/Bax$ gene expression was increased 195% in CJBF treated group onto CYP-treated HHDPCs. In CYP-induced alopecia model C57BL/6 mouse study, promotion of hair growth was observed in the mouse groups treated with the CJBF and CYP-injection. Tissue histological analysis showed the number of hair follicles and the thickness of the epidermis were increased in the CJBF treated groups. Also, to find the possible mechanism, western blot assay was adopted for the tissues of CJBF treated mouse group. Anti-apoptotic $Bcl-2$ proteins were increased, and pro-apoptotic Bax proteins were decreased by 329%. The results led the conclusion that CJBF promotes hair growth and retards the catagen phase in HHDPCs and C57BL/6 mouse model. Therefore CJBF might be a potential new therapeutic source for the prevention of hair loss.