The heading date is known to be controlled by two kinds of genetic constituent, photosensitivity and basic vegetable phase and for the latter, the effect of temperature in early growth period is critical to determine the shortness of vegetative growth periods in plant’s life. A phytotron experiment on 55 rice cultivars, consisting of two ecotypes of rice, indica and japonica was conducted at high and low temperature treatments at early growth stage to investigate the possible role of plant growth stimulus by high temperature to associate with the shortening of heading date. The high temperature during the early growth stage stimulated the rice growth as measured by plant height with the much difference of the growth response between indica and japonica ecotypes. The conclusive finding that these growth stimulus in early growth stage was highly correlated with the acceleration of heading suggested the early growth is, more or less, correlated with the heading of the late growth stage altough we could not conclude the genes for early plant growth stimulus by high temperature is the same genes as the genes for accelerating of heading in the late growth stage of plants.