The inhibitory effect of extracts from 15 edible plants on the protease of human immunodeficiency virus (HIV) type 1 was investigated. Protease activity was determined by incubating the extracts in a reaction mixture containing protease and substrate His-Lys-Ala-Arg-Val-Leu-(p-NO$_2$-Phe)-Glu-Ala-Nle-Ser-NH$_2$ to inhibit proteolytic cleavage. Of various plants tested, the leaves of Cedrela sinensis inhibited the HIV-1 protease by 42% at a concentration of 100$mu extrm{g}$/ml. A major flavonoid isolated from the leaves of C. sinensis, quercetin 3-O-$alpha$-L-rhamnoside showed inhibitory activity of 19% at a concentration of 100$mu$M.