Ionizing radiations are an integral part of conditions of an environment of dwelling of organisms during all history of existence of a life on the Earth. The doses created by a natural back-ground in biosphere for the last 30 years have increased with ~0,1 up to 5,7 rad/year. It is connected to occurrence in biosphere of additional sources of ionizing radiation: radioactive waste products of the enterprises of the nuclear industry, radioactive losses from tests of the nuclear weapon, etc. In this connection special necessity of diagnostics of this kind of pollution has appeared. The soil microflora very sensitively reacts to various changes of soil conditions, therefore it is proved, that microbiological parameters to the greatest degree approach for early diagnostics technogenic damages of soil. Sensitivity and high indicator ability of microorganisms allow to select them as the tool of monitoring of anthropogenic changes in biosphere. The purpose of the present research was to study influence of gamma-radiation on bacteria of chernozem ordinary and restoration of their number in modelling experiments after the influence of gamma-radiation. Object of researches was the arable horizon of chernozem ordinary. The soil samples were taken from the plow layer (0-30 cm) in May 2003 at the training farm Donskoi (Okty-abrskii district, Rostov region). Doses of gamma-irradiation were: 1, 5, 10, and 20 kGy. In air-dried irradiated soil samples determined number of soil bacteria using common methods. After an irradiation of soil modelling experiments for studying restoration of biological properties of soil have been incorporated. The irradiated and control samples of soil incubated in glass vessels at temperature 20-25 Celcium degree and from 60% from a full moisture capacity within 3, 30, 90 and 180 day. After the ending of term incubation in wet samples determined number bacteria on MPA on number colony-forming units. Laboratory - analytical researches carried out by the standard techniques. Modelling experiments put in 3-fold frequency. Analytical definitions of microbiological parameters carried out in 4-15-fold frequency. For bacteria it is not marked unequivocal law of change of number after a radiation depending on dozes and incubation gamma-radiation by dozes 1, 5, 10 and 20 KGy suppresses number of bacteria on 30, 79, 82 and 99,9% in comparison with the control accordingly. The behavior of a population of bacteria is similar under influence of dozes 1 and 10 KGy; 5 and 20 KGy. Feature of influence of a doze 10 KGy will be, that number of bacteria in 3, 30, 90 day of incubation is practically at one level - 12, 12 and 13% and in 180 day - 38% from the control accordingly. In a variant with a doze 1 KGy in 3, 30, 90 and 180 day of incubation - differs not considerably - 89, 81, 62 and 77% from the control accordingly. Number of bacteria in variants with dozes 5 and 20 KGy sharply grows in comparison with the irradiated soil in 3 day - up to 69 and 97% from the control and 30 day incubation - up to 95 and 118% depending on a doze. In 90 day number of ammonifying bacteria is sharply reduced up to 34 and 16% from the control and over 180 day grows a little and becomes at one level - 47% from the control. Thus, gamma-radiation renders overwhelming influence on ammonifying bacteria of cher-nozem ordinary, intensity of overwhelming influence grows with increase in a doze. In modelling experiments of restoration of the irradiated soil the behavior of ammonifying bacteria is similar under the influence of dozes 1 and 10 KGy; 5 and 20 KGy.