Purpose. To determine optimal combination of fertilizing doses, plant density for eight studied hybrids with forming economically valuable part of yield by harvest index calculating.Methods. During 2015–2017, multifactor field experiment was laid and carried out on typical chernozems (Zikrachi village, Kagarlyk district, Kyiv region, Right Bank Forest-Steppe): factor A – hybrid ‘Dniprovskyi 257 CB’, ‘Sigma’, ‘Ragt Alexandra’, ‘Garant’, ‘Kubus’, ‘Moskito’, ‘Sensor’, ‘KВС 381’; factor B – seeding rate 60 and 90 thousands of viable seeds per hectare; factor C – fertilizing doses: N60P45K45; N90P60K60; N120P105K105; N150P135K135. Corn was sown in the period from April 30 till May 4. Accounting of yield was carried out by plots with using a combine. Pre-selected control samples of plants – 10 pieces from two non-adjacent lines in different places of registration area, from two repetitions. Selected plants were analyzed by their structure, determined the mass of by-products and grain. Harvest index was calculated for each option by results of data.Results. A significant variation in the harvest index (HI) depending on weather conditions of the year has been revealed. 2015 was unfavorable for provision of moisture and high temperatures, which led to violation of flowering, fertilization and grain formation. Generative organs were not formed on some plants or significant partial grain forming was observed. That’s why, in terms of low yields and a disproportionately high biomass, HI in 2015 was the lowest compared with other years – 0.36–0.43. In the favorable year 2016, high yield of grain and biomass was formed – HI and its variation was highest compared to other years for all combinations of variants and hybrids – 0.40–0.52. 2017 was also generally characterized as unfavorable in terms of moisture conditions – yield of grain and vegetative mass were rather low, but proportional – harvest index was 0.39–0.44.Conclusions. Harvest index varies significantly in growing of corn hybrids with different standing density, varying doses of fertilizers and weather conditions – 0.36–0.52. Under favourable weather conditions, the index has a significant range of variation. Total mass of plants and yield of grain, even for a certain hybrid, varies significantly depending on fertilizing doses and seeding rate in wet years, and in dry years variation is insignificant. Hybrids ‘Sensor’, ‘Mosquito’, ‘КВС 381’ has a fairly high and stable index over the years. Harvest index is lower for all hybrids and doses of mineral fertilizers with standing density 90 thousands plants/ha compared to 60 thousands plants/ha, excluding hybrids ‘Sensor’, ‘Mosquito’. Harvest index for introduction of high doses of fertilizers, was lower in all years and for all hybrids, with some exceptions.