Two antitumor promoters against tumor promoter-induced Epstein-Barr virus activation were isolated from the leaves of jute (Corchorus capsularis L.). The antitumor-promoting activity was examined by an immunoblotting analysis. Their active components were identified as phytol (3,7,11,15-tetramethyl-2-hexadecen-1-ol) and monogalactosyldiacylglycerol (1,2-di-O-α-linolenoyl-3-O-β-D-galactopyranosyl-sn-glycerol) by spectroscopic data and chemical and enzymatic reactions. The content of the latter in four cultivars of C. capsularis L. and C. olitorius L. was found to vary with the cultivar. The detectable amount of each active component increased by treatment of the leaves with hot water.