An improved growth technology (the arc-fusion method) has been successfully employed to grow large magnesium oxide (MgO) single crystals with an average size of 4-6 cm. Three adjustable graphite electrodes with different electric currents (I-A > I-B > I-C) are applied, which technology is different from the conventional technology (using a uniform current). In addition, a proper control for the efficient use of different currents reduces the number of bubbles in the growth system, which allows us to obtain optically transparent high-purity MgO single crystals. Our present work shows that control of the temperature-gradient field in the whole process is the key to growing high-purity and large MgO single crystals. (c) 2006 Elsevier B.V. All rights reserved.