The electrical conductivity of cross-linked thorium(IV)–alginate complex in the form of circular disc has been investigated as a function of temperature. The Arrhenius plot of logσ vs. 1/T showed a simple parabolic shape at the early stages, followed by a sharply increase in o values with raising the temperature at the final stages. This behaviour was interpreted by the formation of free-radicals at the initial stages, followed by the degradation of the complex at elevated temperatures to give rise to thorium oxide product. The heterogeneous chemical equilibrium for exchange of Th 4+ counter ions in the complex by H + ions has been investigated by titrimetric and complexometric techniques. The thermodynamic equilibrium constant was found to be 26±0.25 dm 9 mol −3 at 25°C. The X-ray diffraction pattern indicated that thorium(IV)–alginate complex is amorphous in nature. Infrared absorption spectra indicated that Th 4+ is chelated to alginate macromolecular chains and displayed υ s OCO − and υ as OCO − in the ranges of 1419 and 1635cm −1 , respectively. A geometrical structure for chelation of thorium(IV) to the functional groups of alginate macromolecule is suggested and discussed in terms of complex stability.