A series of batch and continuous reaction tests using microwave(MW) energy have been executed to take a new opportunities for upgrading a heavy oil. Experimental results show that heteroatoms such as sulfur, nitrogen and oxygen components in a atmospheric residual oil are selectively decomposed at 2.45GHz MW frequency. The maximum removal efficiencies of sulfur and nitrogen were a 37% and 35% respectively when the residual oil was treated with 500watts of MW energy for a very short reaction time in the batch reactor. In the continuous test, the sulfur removal rate was mainly dependent on the MW input power per flow rate of the oil, then the maximum sulfur removal was about 38% at 0.8watts/(g-oil/hr) at residence time 12 min., but nitrogen component was not changed.