Insufficient stability of zeolite is one of the key challenges for application of zeolites in aqueous-phase reactions. In long-term catalytic tests on hydrolysis of ethylene glycol monomethyl ether to ethylene glycol, we found that dissolution of HMCM-49 catalysts could lead to complete transformation to kaolinite. Existence of dissolution equilibriums of Si and Al was demonstrated. In situ growth of HMCM-49 occurred where Si concentration in bulk phase surpasses equilibrium value. This almost completely prevented dissolution and phase transformation of HMCM-49. Dissolution of HZSM-5 catalyst was different. A method by dissolving Si and Al in feed is proposed to solve the problem of zeolite stability in aqueous-phase reactions.