The aim of the study was to analyze the effect of different amounts of mineral fertilization, bacterization of seeds on the leaf surface area formation and the chickling vetch (Lathyrus sativus) productivity. The study engaged six NPK fertilization amounts (0 – the check (control) without fertilizers, N15P15K15, N30P30K30, N15P30K30 + N15 (top dressing), N45P45K45 and N30P45K45 + N15 (top dressing) on two backgrounds of pre-sowing seed treatment (the control, water seed treatment, seed treatment with microbiological preparation Rizogumin, which contains a suspension of nodule bacteria Rhizobium leguminosarum 31 and physiologically active substances of biological origin). The leaf surface area was determined by the cutting method (in the phase of the first trifoliate leaf, budding, flowering, pod formation), which includes the selection of 15 plants, where the leaves are quickly cut off, weighed and their wet weight is determined. After that, cuts are made with a probe of a known diameter, 5 pcs. from every leaf. The mass of all cuts was determined. After determining the surface area of the leaves of each plant, the average plant area was calculated for each variant of the experiment. The average leaf surface area was multiplied by the number of plants per square meter, and the result was multiplied by 10000 to convert it to the average leaf surface area per hectare. The yield accounting was maintained by the method of continuous threshing from the registration plot by a selected combine harvester, with cleaning from impurities, weighing and determining the moisture content of the harvested grain. The maximum leaf surface area (60.8 thousand m2 ha-1) was in the phase of grain filling when N30P45K45 + N15 was added to top dressing and seed treatment with Rizogumin. In the absence of inoculation, the leaf area was 4.1 thousand m2 ha-1 less.