This paper presents the results of studies carried out to estimate the influence of crop rotation, with diversified cereal shares on the humic acid characteristics. The tested range covered humic acids separated from the following soil types: degraded chernozem developed from loess, Orthic Luvisol developed from boulder clay, Orthic Luvisol developed from loess. Samples were taken from the soil arable layer being under many-year crop rotation with a differentiated share of cereals (50 and 100%). The results obtained show that soil use affecred quality indices of humic acids. In the lessive soils under cereal monocultures, an increase of the atomic H:C ratio was observed in humic acids. This allows for a conclusion that the monoculture system causes an increase in the content of aliphatic structures in humic acid molecules or a decrease in the condensation degree of their nuclei. Moreover, a decrease in the optic density of humin solutions given in A₄₆₅ values was found in the humic acids under cereal monocultures which proves a marked direction of changes. In the case of humic acids extracted from chernozem, an analysis of elemental composition did not show any clear differentiation in the crop rotation with a 50% cereal share and a monoculture of cereal plants. The analysis o f optic properties indicates a growth of the optic density (value of the E₄:E₆ ratio decreases) in the variant with a cereal plant monoculture which may suggest growth in the humification of individual humic acids.