It is found out in the studies conducted in Central Chernozem Region of the Russian Federation that along with the decrease of humus content, non-humified organic matter, mobile humus substances, microbial biomass in arable chernozem soils in comparison with virgin lands in unmowed steppe of the Central Chernozem Reservenamed after V. V. Alekhin, the change of the ratio between the components of organic matter takes place. The regularities of agrogenic transformation of the content, composition and nature of mobile humus substances in chernozem soils on arable land are shown. The maximum reduction of non-humified organic matter in arable soils is noted. It is found out that the weight of the light fractions isolated by a granulometric method, is more susceptible to transformation under the influence of anthropogenic pressures than clay ones. This increases the amount of organic carbon in the clay fractions, i.e. organic matter, strongly linked with the mineral part of the soil.