Recently, the urea hydrolysis method has been extensively employed in the fabrication of fine ceramics due to its convenience and controllability of the processes [1–3]. It is also successful in the preparation of lanthanide monodispersed colloidal particles containing single or mixed elements as well as coated colloidal particles [4, 5]. The zirconia powder synthesized by urea hydrolysis can achieve a 100% tetragonal structure owing to its moderate precipitation reaction . In the acid or basic solution, the urea hydrolysis would yield various coprecipitates [4, 5]. Since the urea participates in the reaction of coprecipitation during urea hydrolysis, the resultant product may be different from the gels derived by ammonia coprecipitation. The characteristics of precipitates derived from urea hydrolysis can be further explored by thermal analysis [6, 7]. A systematic thermal analysis was conducted in this study to investigate the crystallization behaviour of hydrous yttria- and ceria-doped zirconia gels with various compositions.