The purpose of the study was to research the effect of se- lective herbicides on soil biological activity and phytotoxicity in the conditions of the steppe zone of Buryatia. The results of the investigation of the influence of four modern herbicides (Magnum Super, Plugger, Balerina, LastikTOP) and their tank mixtures were presented. To determine biological activity of the soil, the method of application of linen fabric (according to Mishustin E.N.) in the soil layer 0-20 cm after 30, 60, 90 days was used. The soil for the assessment of phytotoxicity was selected from a depth of 0-20 cm in 90 days after treatment. As a test object, cress-salad seeds (lat. Lepidiumsativum) were used to test the phytotoxicity of the soil, which gives the most stable and reproducible data, characterized by rapid growth, almost 100 % germination and having clear reaction to the presence of contaminant. In 30 days after treatment, the percentage of tissue weight reduction was approximately at the same level. After 60 and 90 days from the date of ap- plication of herbicides, positive deviation from the control was 9 % and 25 % was respectively noted in the version with the tank mixture Magnum Super, 6 g/hectare + Ballerina 0.2 l/hectare. The results for determining the quantitative values of soil toxicity showed that in the variants using herbicides in tank mixtures with the lowest doses (Magnum Super, 6 g/hectare + Ballerina 0.2 l/hectare and Magnum Super, 6 g / hectare + Ballerina, 0, 2 l/hectare + Lastik TOP, 0.2 l/hectare), the lowest degree of toxicity had been observed, and when using preparations in pure form at the maximum admissible doses, the degree of soil toxicity increased. It was established that effect of herbicides and their tank mixtures depended on the concentration, the temperature regime and the duration of the action.