The characteristics of steroid acyl transferase were studied in the rat brain with (4-14C)-dehydroepiandrosterone(DHEA). The results could be summarized as followings: The enzyme system responsible for the biosynthesis was localized at the microsome fraction. The optimum pH of this enzyme was 4.6 When DHEA was utilized as substrate, $Delta$5-pregnenolone was proved to be a competitive inhibitor. However testosterone was a noncompetitive inhibitor. The acylation at 3${eta}$-hydroxyl group was favored when the hydrophilicity at Cl7 position increased. However, this acylation at C3 was very low when A ring was aromatic. The acylation at Cl7 hydroxyl group reguired an absolute 17${eta}$-conformation.