Need for the introduction of the tropical and subtropical grasses into the southwestern low-land area of Japan has long been stressed. But the monthly mean temperature during winter in Kyushu district where these grasses are thought to be most promissing is almostly lower than their native land. Hence, our problems are existing in the overwintering ability and/or the performance under low temperature conditions in spring and autumn. In this paper, the growth response s to various constant air temperatures of 15 to 33℃ under natural light condition and the chilling injury of seedlings of seven introduced tropical and subtropical grasses, dallisgrass (Dg), Buffel grass (Bg), Scrobic (Sb), Rodd's Bay plicatulum (Rp), Nandi setaria (Ns), Bambatsi makarika-rigrass (Bp) and green panic (Gp) were discussed. Two experiments were conducted in phytotron of Biotron Institute, Kyushu University in summer and late autumn, 1971. 1. The maximum increase of plant height was obtained at the temperature treatment of 25, 30 or 33℃ with respective grass species, but the values were not largely affected within this temperature range (Fig. 1). The reduction of plant height was apparent at 20℃, but the response was less in Ns and Bp (Fig. 1, Table 3). The grasses subjected to 15℃ hardly increased in plant height, and in the summer experiment, all grasses except Dg had chlorotic leaves, indicating chilling injury. All the grasses emerged the maximum number of leaves at 30 or 33℃ (Fig. 2). 2. The tiller formation of most grasses were accelerated at lower temperatures compared with plant height increase or leaf emergence, however, higher tillering rate was observed in Bg, Sb, Ns and Bp even under higher temperature (Fig. 3, Table 2) . 3. The maximum dry matter production of these grasses was recognized at about 30℃ showing high correlation with the plant height increase and leaf emergence (Fig. 4). All grasses grown at 20℃ were depressed in dry matter production, however, the response was relatively low in Ns and Bp (Fig. 4, Table 3). 4. Total-N content was lower and CWC content was higher under higher temperature treatments than under low temperature of 20℃ and there was no remarkable difference within the higher temperature treatments. In Gp and Bg, high dry matter production species, total-N content was low and CWC was high. But these values may be affected more by the growth stage and dry matter accumulation than the direct effect of temperature (Table 1). 5. The rate of decrease in leaf chlorophyll concentration of Sb, Rp and Ns was low at 15℃, indicating the chilling resistance of these species. In cases of other grasses, however, ranking of hardiness was not possible according only to this rate (Table 4) . 6. Optimum temperature for the growth of these tropical and subtropical grass species was shown to be about 30℃. Though at 20℃, sub-optimum, all the grasses were able to grow, but at 15℃, most grasses scarcely grew and were injured. 7. There were differences in growth responses to the temperatures, especially to the low temperature and in chilling injury between the experiments conducted in summer and in autumn. And the differences were assumed to be related closely to the pretreatment conditions of growth and to the day-length and the light intensity during the experimental periods.