Productivity of napiergrass (Pennisetum purpureum Schumach cv. Merkeron), in terms of annual yield (DMY), crop growth rate (CGR) and efficiency of solar energy utilization (Eu) for herbage dry matter in the first year under a heavy nitrogen supply, was compared among Tokyo, Nagoya, Fukuoka, Miyazaki, Naha and Iriomote. In the plants, grown without cutting during the growing season, the values of DMY, CGR and Eu were generally higher than those in most of the other crops at each site, and the regional differences in DMY and CGR showed no definite relationship with the regional differences in the levels of climatic factors, although the higher the solar energy input, the lower the Eu value. However, the productivity of the second growth after a cutting in August, was lower in the northern regions, due to lower temperatures.