Contribution of clay mineral phase (<2 µm) and organic matter to the cation exchange capacity (CEC) of two clayey soils (gleyic black earths from Gniew) was investigated. The XRD analysis showed dominance of illite and mixed layer illite/smectite as well as the presence of smectite, chlorite and trace of kaolinite in the clay fraction of studied soils. CEC of the soils ranged between 22.08-32.64 cmol(+)/kg. After removal of organic matter with 30% H₂O₂, CEC the above values decreased significantly. However, the CEC of organic and inorganic components is not an additive. This may be explained by the fom1ation of organo-mineral complexes, which might lower the CEC of the soil as a whole.