Solutions of different MOH mineralizers (M = Li+, Na+, K+ and (CH3)(4)N+), with concentration level changing between 0.01 to 3.0 M, were utilized for the crystallization of zirconia gel under hydrothermal conditions at 110 degrees C for 7 days. An increasing crystallization rate of zirconia resulted at increasing concentration of each basic mineralizer. The corresponding and progressive diminution in the crystallite size of products determined the formation of monoclinic, tetragonal and cubic sequence of zirconia. The crystallization rate of gel was found to depend also on the nature of mineralizer solution; higher cationic radius of MOH mineralizer, lower crystallization rate was observed. A nucleation and growth mechanism is proposed for the crystallization of zirconia gel during the hydrothermal treatment in the presence of different basic mineralizers.