The dissolution behaviors of Ta2O5, Nb2O5 and their mixture in KOH and H2O system were investigated. A L9(34) orthogonal design was used to study the effects of reaction temperature, mass ratio of KOH to Ta2O5, and reaction time on the dissolution rate of tantalum. It was found that the effect of reaction temperature on the dissolution rate of tantalum was much greater than that of the other factors. The results of factorial experiments showed that Ta2O5 was mainly transformed into insoluble potassium tantalate at low temperature (350 °C) and transformed into soluble potassium tantalate at high temperature (450 °C). The insoluble potassium tantalate was analyzed by XRD, which was proved to be KTaO3. Differently, almost all Nb2O5 was transformed into soluble potassium niobate at 350-450 °C. As for the mixture of Ta2O5 and Nb2O5, the dissolution rate of tantalum increased and the dissolution rate of niobium decreased as an interaction existed between niobium and tantalum. And increasing the mole ratio of Nb2O5 to Ta2O5 in the mixture was beneficial to the dissolution of both Ta2O5 and Nb2O5. In addition, the mechanism of the interaction between niobium and tantalum was also investigated through phase and chemical analysis.