To investigate biological activity of noni extracts treated with HCl and trypsin, we measured the antioxidant activity through vitro assay and cellular system. Both water and lipid soluble fraction of noni extracts dose-dependently scav­enged DPPH radical. Superoxide scavenging activity of lipid soluble fraction after treating HCl and trypsin was significantly more potent than those of other fractions in NBT/xanthine oxidase assay, which suggests that antioxidant activity of noni extracts was increased by the treatment with HCl and trypsin. In antioxidant assay using RBL 2H3 cells, water soluble frac­tion of noni extracts had little effect on silica-induced reactive oxygen species generation, whereas lipid soluble fraction inhibited in a dose dependent manner. In non-treated noni extracts, effect of water soluble fraction on silica/$CuSO_4$-induced lipid peroxidation was more potent than that of lipid soluble fraction. However, the effects of noni extracts were reversed in noni extracts treated with HCl and trypsin. These data suggest that water soluble substances may be converted into lipid soluble substances by the treatment with HCl and trypsin. From the above results, it is suggested that lipid soluble fraction of noni extracts contain antioxidant used in vitro assay and RBL 2H3 cellular system. Such an effect of noni extracts may be increased by the treatment with HCl and trypsin.