Abstract <p>In this work, the results of a study on the extraction and preconcentration of trace amounts of thorium(IV) and uranium(VI) with a polymer chelating sorbent are presented. For the sorption-photometric determination of Th(IV) and U(VI), a modified sorbent based on a copolymer of maleic anhydride with methacrylic acid is proposed. The static exchange capacity of the obtained sorbent for the K⁺ ion was 9.3&#xa0;mmol/g. The optimal sorption conditions were determined. At pH 4, the degree of sorption passes through a maximum. With an increase in the concentration of Th(IV) and U(VI), in the solution, the amount of absorbed metal increases, and at a concentration of 8 × 10^–3 M it becomes maximum (<i>c</i>_Th(IV) = 696 mg/g and <i>c</i>_U(VI) = 596 mg/g). The sorption isotherm of Th(IV) and U(VI) with the synthesized sorbent was constructed. The dependence of sorption on time and ionic strength of the solution was investigated. Sorption equilibrium is achieved within 1 h of contact of the solution with the sorbent. It was found that at pH 4, the maximum metal sorption is achieved using 50 mg of the sorbent. The effect of different mineral acids (HClО₄, H₂SO₄, HNО₃, HCl) with the same concentrations on the desorption of Th(IV) and U(VI) from the sorbent was studied. The results showed that the maximum desorption of Th(IV) and U(VI) occurs in chloric acid. The developed method was applied to determine microquantities of Th(IV) and U(VI) in water taken from the well of the Balakhany oil and gas production department (Azerbaijan) with preconcentration.</p>