For the development of anti-AIDS agents, thirty-seven methanol extracts of Korean plant materials were tested for their inhibitory effects on human immunodeficiency virus type-1 (HIV-1) protease. Extracts of seven plants showed more than 30% inhibitory activities on HIV-1 protease at a concentration of . The bark of Berchemia berchemiaefolia, the leaf of Lindera erythrocarpa and the whole plant of Siegesbeckia pubescens exhibited significant inhibititory activities on HIV-1 protease with 56.2, 50.8, and 46.6%, respectively.