As sulfur dioxide is oxidized on vanadium catalysts, phase transitions may occur in the catalyst active component, which are related to the crystallization of vanadium(IV) compounds resulting in the decrease of catalyst activity. In this paper, we report on the peculiarities of reversal process such as crystal phase dissolving, which is aimed at catalyst regeneration. We have studied how crystal phase dissolving rate depends on dissolving conditions such as temperature, gas mixture composition as well as on the conditions of crystal phase formation. Dissolving dynamics is described by a mathematical model, which was earlier suggested for the processes of crystal phase generation and growth.