A cubic niobic acid (C-NbA) was synthesized by Li+/H+ ion exchange reaction with an 8 M (mol dm(-3)) nitric acid solution from LiNbO3. The LiNbO3 was obtained by heating a mixture of Li2CO3 and Nb2O5 with molar ratio of 1:1 at 900 degrees C for 24 h. X-ray diffraction pattern of C-NbA was indexed to a cubic structure (space group Im3), with the lattice constant a(0) = 7.6445 Angstrom (Angstrom = 100 pm). The C-NbA product showed an exchange reaction equiv alent to one proton per one Lit in a mixed solution of lithium nitrate and lithium hydroxide. The pH titration curves of C-NbA on the Li+/H+ exchange system indicated a weak monobasic acid. C-NbA showed high uptake for lithium ions, whereas no appreciable amount of uptake was observed for other alkali metal ions in the pH range 4-12. An extremely high selectivity was found for lithium ions, and the separation factor (alpha) of lithium ions to other alkali metal ions was higher than 10(3).