Methane fermentation of napiergrass (Pennisetum purpurum Schumach, cv. Merkeron) in the first year of growth at several places varying in the climate (Tokyo, Nagoya, Fukuoka, Miyazaki, Naha and Iriomote Island) was investigated. The gas evolution rate examined using fresh material of the plant at 37°C for 7 days, was 542 L per kg based on dry matter for leaf blade, 352 L for stem with leaf sheath and 342 L for dead parts, on an average for those harvested in above six areas. The gas volume evolved from the stem decreased as the growing days and the dry matter yield increased. The relation between dry matter yield and gas volume evolved from the whole shoot was similar to that observed for stem. The methane content of gas produced from any materials examined was estimated to be about 60% in volume. Thus the average annual yield of methane, if the whole shoot is fermented, will be be about 7, 000 m3 ha-1 in any place of the areas tested. This is greater than the values obtained for several other C4-and C3-forage crops and grasses, indicating that napiergrass is a useful plant for production of not only forage but also methane as a fuel.