Copolymerization using microwave energy, has many advantages such as notable time savings, solvent savings and cost savings. The main reason is that microwave energy has internal heating effect in dielectric material. In this study, the styrene/scrylonitrile solution copolymerization was rapidly carried out using microwave energy. The irradiation power of microwave was regulated at the 130, 195 and 260 W, and irradiation time was varied in the range of 10 to 140 min. The conversion of SAN decreased as mole fraction of styrene, and increased. The highest conversion appeared at 0.2 mole fraction of styrene, the average molecular weight of SAN was very large at this condition. The conversion of SAN (mole fraction of styrene = 0.2) increased as irradiation time increased, and the maximum conversion was 40.92% at 130 W of microwave irradiation power, and 120 min of irradiation time. This result has shown that the conversion was higher and copolymerization time was shorter than a conventional heating method (no use of microwave energy). From the calculated reactivity ratio with Kelen-Tudos and Fineman-Ross method, the SAN was deduced to the alternating copolymer type. In comparison with a thermal heating method, the introduction of microwave energy shorened copolymerization time and improved copolymerization efficiency.