Using herbicides has a significant effect on different microbial processes in the soil and, depending on the type of soil and on the used dose, they may modify the quantity of their biomass for a certain period of time. The aim of this investigation was to trace and identify the effects of the herbicide napropamide on the principal groups of microorganisms in the soil during the production of seedlings for broadleaf tobacco, as well as the impact of weather conditions on this process. Soil samples were taken on the 1-st, 7-th, 15-th, 30-th and 60-th days after input of the product. It was found out that Devrinol 4F has a direct influence on major groups of soil microorganisms. Thirty days after treatment this effect is insignificant.