A study on the decomposition of zinc cobaltate was made to improve the extraction of cobalt from the cobalt cake (Cobalty-Nitroso-β-Naphthol) which is produced as by-products at the hydrometallurgical process of zinc. It has been reported that zinc cobaltate was formed during the roasting process of the cobalt cake. Zinc cobaltate was prepared from the nitrate mixtures by drying them at 200℃ for 9 hrs and heating them at 400℃ for 4 hrs. The final product was ZnCo₂O_(3.962). It was observed that zinc cobaltate was decomposed into ZnO and Co₃O₄in the temperature range of 450-810℃ and Co₃O₄was again decomposed into CoO in the temperature range of 820-890℃, thus gave final products of ZnO and CoO over 920℃. Leachability of cobalt from the decomposed products over 920℃ has been determined in various concentrations of sulfuric acid. It was observed that 97.6% leachability of cobalt in 5N-H₂SO₄was obtained. The reaction order and apparent activation energy of the decomposition of zinc cobaltate was respectively 0.7 and 63.6 ㎉.