Mechanical properties, thermal stability and optical properties of triacetyl cellulose (TAC) films plasticized by three types of plasticizer, triphenyl phosphate (TPP), biphenyldiphenyl phosphate (BDP) and a mixture of TPP and BDP have been investigated in order to find the optimum plasticization condition for a protective film application in LCD. Mechanical properties such as modulus, tensile strength and elongation at break, and thermal property were significantly distinguished according to the type of plasticizer. TPP worked as the most effective plasticizer for TAC in the viewpoint of the mechanical properties. TAC/TPP showed the largest increase in elongation at break and the biggest reduction in the glass transition temperature at the same plasticizer level. However, TPP had the worst thermal stability. A mixture of TPP and BDP achieved the compromising plasticization to produce the moderate mechanical properties and thermal stability of TAC films for protective film application in LCD.