The investigation not the storage root yield in sweet potatoes was carried out using different compositions of mineral nutrients by gravel culture. Roots were divided into two different functional parts, storage roots and feeder roots. Culture solutions of different concentrations were applied to the feeder roots and identical soil conditions with method the storage roots. 1) The nitrogen content of culture solution used for feeder roots greatly affected the thickening of the storage root. Treatment with potassium-containing solution had less effect on the storage root growth, except in the high nitrogen treatment plot. 2) A close relationship was recognized between the nitrogen content in leaves and the dry weight ot the storage root; the optimum nitrogen content for the dry matter production of storage roots was 3.0-3.7% throughout their growth stage. 3) A certain degree relationship was recognized between the storage root dry weight and K2O/N ratio in the storage root. Increse in the K2O/N ratio favorably affected the growth of the storage root in the high-nitrogen concentration plot; whereas in the low-nitrogen plot an increase in the K2O/N ratio adversely affected the storage root growth. 4) These results seem to suggest that nitrogen had the primary effect for promoting thickening of the storage root, and high potassium dosage had a marked effect on storage root growth in the case of excessive nitrogen application.