The enzyme steroid $5{alpha}-reductase$ is responsible for the conversion of testosterone into the most potent androgen dihydrotestosterone (DHT). In man, this steroid acts on a variety of androgen-responsive target tissues to mediate such diverse endocrine processes as male sexual differentiation in the fetus and prostatic growth in men. Androgen levels in the prostate may influence carcinogenesis in this organ. The use of a $5{alpha}-reductase$ inhibitor, finasteride, in the chemoprevention of prostate cancer is being evaluated in a clinical trial and have been used successfully for treatment of benign prostatic hyperplasia. Therefore, for the discovery of $5{alpha}-reductase$ type 2 inhibitors, we have evaluated the inhibitory effects of solvent fractionated extracts of natural products on $5{alpha}-reductase$ type 2 activity. We have tested approximately 80 kinds of natural products after partition into n-hexane, ethyl acetate and aqueous layers from 100% methanol extracts of plants. The ethyl acetate fractions of Perilla sikokiana $(seed,;IC_{50};:;6.2;ug/ml)$, Sophora flavescens $(root,;IC_{50};:;8.9;ug/ml)$, and Angelica tenuissima $(root,;IC_{50};:;11.7;ug/ml)$ revealed inhibitory effects on $5{alpha}-reductase$ 2 activity in LNCaP cells. The effective ethyl acetate fractions of Perilla sikokiana, Sophora flavescens, Hydnocarpus anthelmintica, and Angelica tenuissima were subfractionated by column chromatography and tested. The subfractions $F4;(IC_{50};:;1.1;ug/ml),;F5;(IC_{50};:;2.0;ug/ml),;and;F6;(IC_{50};:;5.8;ug/ml)$ of the ethyl acetate fraction of Perilla sikokiana and the subfraction $F8;(IC_{50};:;5.3;ug/ml)$ of the ethyl acetate fraction of Sophora flavescens displayed greater inhibition of $5{alpha}-reductase$ type 2 than did finasteride in LNCaP cells. These active fractions are under the process of further sequential fractionation to find the effective pure compounds against $5{alpha}-reductase$ 2 activity.