AbstractDetermination of conductance, pH, Spectrophotometry, and Refractive‐Index measurements of a series of mixed solutions of uranyl nitrate and thorium nitrate, indicate the existence of one definite complex‐compound in the solution namely\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Th(NO}_{\rm 3} {\rm)}_{\rm 4} - {\rm UO}_{\rm 2} ({\rm NO}_{\rm 3})_2 $$\end{document}Monovariation method of NNYARand PANDE(1), has been followed in the preparation of the solution and in the investigation of properties. Aqueous solution of the uranyl nitrate and thorium nitrate were prepared in such a way that the concentration of uranyl nitrate was kept constant, while that of thorium nitrate was varied systematically, and the physico‐chemical properties recorded. When the values are plotted against the concentration of thorium nitrate curves are obtained with the specific breaks. The kink occurs at exact stoichiometric ratio of the concentrations corresponding to the compound noted