The impact of phosphates on organic matter release from peat-muck soils was shown. Peat-muck samples were described among others by water adsorption index, content of amino acids, bulk density, pH, and ash. On the base of obtained data, studied samples were characterized in terms of variable surface charge and possible changes in surface properties of humic acids which might have been under phosphates influence. Nature of studied humic acids were defined by elemental analysis. The release of dissolved organic matter from calcium forms of the humic acids was significantly affected by concentration of added salt. Generally, an increase in concentration of phosphates resulted in increasing of humic substances released to the solution up to 0.025 mol dm-3 of the added salt. At very low, initial phosphate concentration, the secondary coagulation of dissolved organic matter was observed. Potentiometric titration curves of humic acid solutions without addition of phosphate ions showed that studied organic matter was differentiated in relation to variable surface charge. However, titration curves of humic acids with additions of different phosphates concentrations were identical what could indicate that under experiment conditions, phosphates did not influence on structure of humic acid surface.