In the present study, the microstructural evolution and high temperature deformation behaviours of 8 mol% Y2O3 stabilized cubic zirconia (8YCSZ) containing up to 10 Wt% SiO2 is investigated. The experimental results show that the SiO2 doped specimens sintered at 1400 degrees C contain only the cubic crystalline phase and SiO2 has the very limited solubility of 0.3 wt% in cubic zirconia. This suggests that only small part of the SiO2 dissolves in the cubic zirconia and the rest of SiO2 segregates at grain boundaries and multiple junctions as amorphous (glassy) phase. This glassy phase prevents the grain growth by minimizing grain boundary energy and mobility, which results from solute segregation at the grain boundary and its drag. The deformation of the undoped 8YCSZ is characterized by large strain hardening with limited elongation. This is mainly due to severe grain growth during high temperature deformation. The addition of the SiO2 results in a decrease in strain hardening and enhanced tensile elongation. These effects have been further improved with the increase of the SiO2 addition reaching the elongation to failure of 152% for 10 wt% SiO2 doped specimen in tension at a temperature of 1400 degrees C and strain rate of 1.3 x 10(-4) s(-1). The decreased strain hardening and increased ductility in the SiO2 doped specimens are due to the segregation of amorphous glassy phase to the grain boundaries, thus hindering grain growth and facilitating grain boundary sliding, which is the primary mechanism of deformation in fine grained materials at high temperatures. (C) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.