The investigation of crown photosynthesis produc-tivity (CPP) of woody plants is necessary for character-izing the receipt of carbon balance and its subsequent comparison to the items of expenditure: breath and growth. In the Baikal forest-steppe zone, near 80 km to the northeast of Irkutsk, between 1976 and 1986 by the method of infrared gas analysis, CO2-exchange of the needles of adult pine trees was studied. At the same time, ecological factors of heat and moisture supply of the environmental and the needles' biomass were rec-orded. Day productivity of photosynthesis (DPP, mg CO2/g) was determined from the intensity of visible CO2 input; according to the results of 30-70 DPP measure-ments represented seasonal dynamics of two-year-old needles photosynthetic productivity. The changes in DPP were due to the passage stages of seasonal de-velopment by Scots pine trees: phenophases of bud buds swelling, shoots growth, needles growth, summer vegetation. By finding average daily photosynthesis rate of two-year needles depending on the orientation along the sides of the light, model pine trees crown was zoned according to photosynthetic activity. The algorithm for calculating CPP included the data on DPP of two-year-old needles in the middle, upper and lower parts of the crown, coefficients for determining DPP of the needles of the 1-st, 3-rd-6-th year of life and the data of differ-ent-aged needles biomasses in all parts of pine crown. According to obtained results, CPP of model pine trees in the years of the registration of CO2-gas exchange differed more than twofold. For the following years, when visible photosynthesis of the needles was not measured, in the algorithm for the determination of pine CPP were calculated DPP of two-year-old needles of middle part of pine crown using the dependence of DPP from available soil moisture in root layer 50-centimeter or moisture coefficient.