To estimate the possibility of napiergrass for cultivating as a perennial in southern Kyushu, the overwintering ability, as assessed by the percentage of overwintered plants (POP) in early May, was determined for several cultivation factors. To maintain high overwintering ability, it was important to conduct the final cutting just before the first frost date at about 20 cm above ground surface. The effects of planting date from spring through summer and of the year after establishment within 3 years on POP were small. On the contrary, the differences in POP among years and among different altitudes were large. The variety of Merkeron had a superior overwintering ability in comparison with Wruk wona. The relationship between the minimum daily temperature during the overwintering and POP was positively logarithmic in two varieties of Merkeron had POP exceeding 50% in more than half the areas in Miyazaki, even under the coldest winter of the seven seasons examined, suggesting its stable overwintering ability in southern Kyushu.