In the Southern part of Russia sands and idiosyncratic soils, equivalent to sands, can be found in Rostov, Astrakhan and Volgograd regions as well as in Dagestan and Kalmykia. A permanent peculiar feature of sands is their own special zonal vegetation. Among the soil diversity of Rostov region sands occupy 220,000 hectares, that is why studies of biological properties of sandy soils attract a lot of attention and interest. The purpose of the present study is to estimate the microbial flora numerosity in sandy soils compared to zonal soils surrounding them. Sandy soils and southern black humus soils of the northern part of Rostov region were taken as the subject of research. Southern black humus soils refer to basic zonal soils of Rostov region. Those are carbon-bearing soils. Sandy soils refer to noncarbonate intrazonal soils. Soil samples were taken during 2004 from the sands under pine-tree plantations and under a plot with herbaceous vegetation. Samples of the southern black humus soil were collected under a virgin feather-grass steppe. Numerosity of microorganisms was determined by way of inoculation of solid medium. Numerosity of bacteria was determined on meat-and-peptone agar and microscopic fungi - on acidified Czapek's medium. Making a comparison of biogenic nature of sandy soils with the zonal soils of this region (southern black humus soil) it was discovered that bacteria numerosity in the topsoil is almost 4 times less than that in the southern black humus soil. It is connected with the low content of humus in sandy soils (1,22%) compared to black soils (6,94%) as well as with bad hydrophysical properties of sandy soils. Completely percolating water filtration and low water retention lead to sand soil humidity of 2-3% in May, this figure being by 6-9 times lower than that of black humus soil. Numerosity of microorganisms decreases down the soil profile, and that is connected with reduction of humus content. Differences in numerosity of microscopic fungi in soils under research are manifested to a lesser degree. In horizon AD of the southern black humus soil the numerosity of microscopic fungi was discovered only by 1,2 times more than in grey sandy soils. Their profile distribution is similar to bacteria distribution. The biogenic character, considering the profile depth in sandy soils, compared to the zonal soil is 30% less in microscopic fungi and 52% less in bacteria. The results of researches showed that there exist differences in microbial flora numerosity between samples of the same soil taken from under different types of vegetation. In sands under the herbaceous vegetation bacteria numerosity is 3 times more than in sandy soils taken from under the forest. At the same time the numerosity of microscopic fungi in the topsoil taken from under the forest vegetation was almost 2 times higher. But this index in the soil profile under the pine-tree vegetation is significantly stronger. That is why on conversion the data to the entire profile, it was discovered that sandy soils under herbaceous vegetation are 6 times richer in bacteria numerosity and only by 30% richer in fungi numerosity. It is connected with higher enrichment of sandy soils under herbaceous vegetation in organic matters. The humus content here is 2,5 times higher than under forest vegetation. In 2004 samples were taken three times (spring, summer, autumn) and that permitted to examine the seasonal dynamics of microbial flora numerosity in sandy soils. Microbial flora numerosity peak was evidenced in October almost in all horizons. It was obviously connected with increased humidity in autumn. Fungi numerosity in different horizons varies significantly. In the topsoil the numerosity (May-July-October) grows almost in a linear fashion. In horizon AB the activity recession of microscopic fungi was evidenced in July. In horizon B differences in the seasonal dynamics were not evidenced, and that is probably connected with more sustainable conditions. Same tendencies were evidenced in the dynamics of bacteria numerosity. In summary, there was made differentiation in microbial flora numerosity between soils of different types (sandy and southern black humus soils) as well as every bit as important differences in the soil of the same type (sandy soils) but taken from under different types of vegetation.