<p>Herein, a sub-micron lanthanum zirconate ceramic (La₂Zr₂O₇, LZO) with a pyrochlore structure was prepared by the sol-gel and high temperature sintering methods. The corrosion behavior and mechanism of calcium-ferrum-alumina-silicate (CFAS) powder (33CaO: 10FeO_1.5: 13AlO_1.5:44SiO₂) on the sub-micron LZO ceramic at 1673 K was investigated. The results indicate that the average grain size of sub-micron LZO ceramic was 895 nm. The CFAS melt rapidly diffused into the interior of the LZO ceramic wafer and reacted with it to generate high melting point rod-shaped Ca₂La₈(SiO₄)₆O₂ apatite and <i>m</i>-ZrO₂ phases, which can effectively hinder further diffusion of CFAS melt, resulting in a slow increase in corrosion depth with corrosion time. After 30 h of CFAS corrosion at 1673 K, the corrosion depth of the LZO ceramic wafer was only 160.3 µm, demonstrating its excellent high-temperature resistance to CFAS corrosion.</p>