The effect of temperature during the ripening period on the seed yield and its quality was investigated using cv. Miyagishirome. The temperature treatments were composed of eight plots: five day/night temperature plots (30°/25°, 30°/20°, 25°/20°, 25°/15° and 17°/12°C, day and night temperatures being constant, respectively), two gradual temperature change plots (the diurnal temperature gradually changes along with sine curves designated as 25°/20°and 17°/12°, the daily mean temperature being almost the same to the respective 25°/20° and 17°/12° plot) and outdoor control (average daily mean temperature was about 21°C). The results obtained are summarized as follows: 1. The dry weight per plant was in the following orders: 25°/20°>30°/25°≥17°/12° in case of 5°C daily range, and 25°/15°>30°/20° in case of 10°C daily range. When the day temperature was the same, the dry weight per plant grown under 10°C lower nights was greater than that under 5°C lower nights. There was little difference in dry matter production between the gradual temperature change plots and the suddenly change plots. The dry weight of the outdoor control was almost the same as that of 25°/20°. 2. Seed yield per plant was greater at 25°/15° and 30°/20° plots, followed by 25°/20°, 25°/20°, 30°/25° and outdoors in that order, and very small both at 17°/12° and 17°/12°. Numbers of pod and seed per plant tended to increase with increase of temperature in case of 5°C daily range, while those of 25°/15° and 30°/20° were almost same. Numbers of pod and seed of 10°C daily range were greater than those of 5°C daily range when the day temperatures were same, and those of the outdoor control were similar to those of 25°/20°. 100-seed weight was very great at 25°/20° and 25°/20°, followed by 25°/15°, 30°/20°, outdoor control, 30°/25° in that order and those of 17°/12°, 17°/12° were extremely small. 3. N, K, TAC (Total Available Carbohydrate) and seed oil accumulation perplant were paralleled with dry matter accumulation in response to temperature. P accumulation tended to increase with increase of temperature. At maturity most of N, P, K and TAC accumulated in seeds, Mg+Ca in pod shells and Fe and Na in roots, respectively. The concentration of Fe and oil in seeds tended to increase and that of carbohydrate to decrease with increase of temperature. Saturated fatty acids in seed oil such as palmitic, stearic and oleic acid with one double bond tended to increase and other unsaturated acids such as linoleic and linolenic to decrease with increase of temperature. 4. The larger seeds ripened outdoors or at 25°/20°, 25°/15° and 30°/20° showed a higher germination percentage. 5. In the regime of this experiment, day temperature of 25° to 30° with 10°C daily range during the ripening period seemed to be optimum for dry matter accumulation, nutrient absorption, seed yield, and seed characters, suggesting that the optimum temperature for ripening is a ittle lower than that for vegetative growth.