In order to design various drying equipments of food materials, it is necessary to determine the drying-rate equations. In a former paper1～3), we studied the over-all drying-rate equations of root vegetables under the heated air-flow dryer. To improve the process, a faster dehydration method by using various heating methods or pre-treatment methods of samples is required. In this paper, we studied the over-all drying-rate equations on the drying of potatoes by microwave energy and of bored ones by heated flowing air. In the drying-rate equation on the drying by microwave enegy, we obtained it in the initial drying region only. The values of the orders in the rate equation are much larger on the drying by microwave energy than the ones obtained by heated flowing air. The results for the unbored and bored potatoes on the drying by heated flowing air did not differ from each other in these experimental conditions. The results of the microwave drying obtained are usuful for later promising experiments of the pre-treatment of potato using microwave energy.