Abstract:To study the chemical constituents of the 95% ethanol extract of Psidium guajava.Compounds were separated by using a combination of various chromatographic methods including silica gel, D101 macroporous resin, ODS, Sephadex LH-20 and preparative HPLC.Their structures were elucidated by physicochemical properties and spectral data. Eighteen compoundswere isolated and identified as(+)-globulol(1), clovane-2β,9α-diol(2), 2β-acetoxyclovan-9α-ol(3),(+)-caryolane-1,9β-diol(4), ent-T-muurolol(5), clov-2-ene-9α-ol(6), isophytol(7), tamarixetin(8), gossypetin(9), quercetin(10), kaempferol(11), guajaverin(12), avicularin(13), chrysin 6-C-glucoside(14), 3‘-O-methyl-3, 4-methylenedioxyellagic acid 4‘-O-β-D-glucopyranoside(15), p-hydroxybenzoic acid(16), guavinoside A(17)and guavinoside B(18). Compounds 2-9 and 14-16 were isolated from this plant for the first time.The ethanol extract showed 61.3% inhibition against the proliferation of colon cancer cell line SW480.