trans-Cinnamic acid, a natural product isolated and purified from the barks of Cinnamomum cassia, with phytotoxic, anti-diabetic, antixcancer, antioxidant and anaesthetic activities, is cell differentiation inducer, protein isoprenylation inhibitor, shows a significant radio-protective effect by reducing the DNA damage induced by X-rays, inhibits feeding by detritivores, and the diphenolase activity of mushroom tyrosinase and the inhibition is reversible, the IC 50 values are estimated to be 2.10, 0.50 and 0.42 mM, respectively.