Humic substances (HS) are natural compounds, the formation of which occurs in natural environments as a result of chemical and biological decomposition. HS accounts for 60% to 80% of organic matter in soil and aquatic environment. Therefore, we obtained samples of HS isolated from low-mineralized sulphide mud deposits of Tuzkol Lake (Republic of Kazakhstan) were obtained. HS samples have been characterized by instrumental methods: EPR spectroscopy and amperometry. Analysis of the concentration of paramagnetic centers shows that the minimum number of free radicals contains molecules of fulvic acids, and the maximum number of free radicals contains molecules of humic acids (HA) of peloids. The antioxidant activity and bioavailability of humic preparations in the form of sodium humates depending on the concentration of HS have been investigated. The information obtained indicates that HS have antioxidant activity and bioavailability, the value of which increases when the concentration of the solution grows. Dialysis of silver humate has been carried out in the presence of dimethyl sulfoxide (DMSO) at concentrations of 0.1; 1.0; 5.0 and 10% w/w. For HA and silver humate, a 10% concentration of DMSO is optimal, which allows a maximum yield of peloid preparations and a 1.6-fold increase in permeability. Dialysis of silver humate is 1.2 times more intensive than dialysis of HA. It has been shown that the change in the total content of antioxidants in various fractions of humic substances increases in the series; fulvic - humic – gimatomelanic acids.