The myogenic differentiation of C2C12 myoblast cells is induced by the novel androgen receptor (AR) partial agonist, (17α,20E)-17,20-[(1-methoxyethylidene)bis-(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK11), as well as by dihydrotestosterone (DHT). YK11 is a selective androgen receptor modulator (SARM), which activates AR without the N/C interaction. In this study, we further investigated the mechanism by which YK11 induces myogenic differentiation of C2C12 cells. The induction of key myogenic regulatory factors (MRFs), such as myogenic differentiation factor ( MyoD ), myogenic factor 5 ( Myf5 ) and myogenin , was more significant in the presence of YK11 than in the presence of DHT. YK11 treatment of C2C12 cells, but not DHT, induced the expression of follistatin ( Fst ), and the YK11-mediated myogenic differentiation was reversed by anti-Fst antibody. These results suggest that the induction of Fst is important for the anabolic effect of YK11.