The present invention relates to a composition for stimulating hair growth or preventing hair loss, which contains a conditioned medium or extract of neural stem cells (NSCs) isolated from the ventricular zone of the human brain, and to a preparation method thereof. The conditioned medium or extract of neural stem cells according to the present invention contains various growth factors and cytokines, and thus has an excellent effect on the stimulation of hair growth. Thus, it is useful for hair growth stimulation and hair loss prevention.