The aim of this study was to record corrosion behaviour of ZTA and ATZ ceramics under hydrothermal conditions and under influence of boiling acids. Ageing was performed for 30 h and for 100 h in an autoclave at 134 °C and at a pressure of 2 bar. The sample surface was characterised with the help of measurements of surface finish, strength and microhardness, as well as by means of determination of wetting angle of contact. Leaching behaviour was analysed by means of scanning electron micrographs and weightings. The results of all tests with ZTA and ATZ ceramics performed in connection with this survey showed positive results, i.e. neither acid treatment nor hydrothermal ageing resulted in significant changes of properties.