Hydroxylation and glycosylation of cinnamic acid, p-coumaric acid, caffeic acid, and ferulic acid were investigated using cultured plant cells of Phytolacca americana as biocatalysts. Regioselective hydroxylation at the 4-position of cinnamic acid and 3-position of p-coumaric acid was observed. Although cinnamic acid was transformed to mono-glucoside products, di-glycosylation occurred in the case of the biotransformation of p-coumaric acid, caffeic acid, and ferulic acid.