An optimal grade transition policy is essential when several grades of polymers are produced in the same continuous stirred tank reactor (CSTR). We discuss an optimal grade transition to minimize the amount of raw material assumption during the transition operation as well as to shorten the transition time. Through case study of a free radical styrene polymerization in a pilot CSTR, we show that a combination of regulatory control and dynamic optimization is very effective for the optimal grade transition operation of continuous polymerization reactor.