The life history and matter economy were studied on an evergreen herb, Pyrola japonica Klenze, population growing on the floor of a deciduous forest in a warm temperate region, central Japan. Seasonal changes in standing crop, bulk density and reserve substance of each organ and in leaf area were investigated over a year. Monthly and annual net production of the population were estimated based on the growth in dry weight and the seasonal dynamics of reserve substance. Seasonal peak value of the monthly net production was 16.7 g d.w.m-2 in May. The annual net production was estimated to be 60.2 g d.w.m-2. Two phases were recognized in the annual pattern of development and matter economy of this plant. Phase I, from April to June, was characterized by the development of aboveground vegetative organs and the consumption of reserve substance rrom old organs. Phase II, from July to March, was characterized by the development of reproductive and underground organs, and the accumulation of reserve substance. Phase II was further divided into two sub-phases according to the behavior of the reserve substance and the rate of net production. The production process of the population was compared with those of other evergreen herbs growing on the forest floor in warm temperate regions.