The effects of 12 phytopolyphenols, including 3 catechin derivatives, 8 flavanols, and curcumin, on 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced transformation in mouse fibroblast cells are described. The location of hydroxyl functional groups at 2', 3', or 4' site(s), especially at the 4' site, as in apigenin, fisetin, morin, myricetin, and quercetin, seems essential for anti-TPA-induced transformation, anti-protein kinase C (PKC) activation, and anti-TPA-induced c-jun expression activities. Among the catechin derivatives, those with a cis form structure and with an additional hydroxyl group at the R1 site and galloyl groups at the R2 site, such as epigallocatechin gallate, have stronger inhibitory effects on the above-mentioned biochemical activities. Considering their polarities and chemical structures, these compounds have different oxygen radical absorbance capacity in the in vitro assay. In addition, curcumin also has these inhibitory effects on the above-mentioned biochemical activities and antioxidant activities for peroxyl radical but not hydroxyl radical. In addition to PKC activation, active oxygen species production, and c-jun induction, our data suggest that TPA treatment induces cellular transformation by other unknown routes, because some tested compounds have an inhibitory effect on TPA-induced transformation but have no or a slight inhibitory effect on PKC activation, active oxygen species production, and c-jun induction.