Abstract: Proposed is an inorganic ion-exchanger, which is selective to lithium and constituted a non-stoichiometric compound in the form of solid particles of a polymeric aqua-oxo-hydroxo complex represented by the following general formula: HaNbO(2.5+0.5·a).cZrO2.dH2O, wherein: “a” is a number ranging from 0.5 to 1.5, “c” is a number ranging from 0.01 to 1.0, and “d” is a number ranging from 0.1 to 2.0. The complex has a total ion exchange capacity of at least 3.5 meq/g and an ion-exchange capacity specifically to lithium of at least 2.5 meq/g. This ion-exchanger is intended for selective extraction of lithium from lithium-containing natural and industrial brines.