The use of ceramic oxide coatings on silicon nitride is one method to improve its alkali corrosion resistance. Four oxide coatings, including (Ca-0.6, Mg-0.4) Zr-4(PO4)(6) (CMZP), zirconia, mullite and alumina, were examined. These coatings were applied on Si3N4 using both sol-gel and dip coating techniques. The coated and uncoated samples were exposed to sodium molten-salt and sodium-containing atmospheres at 1000 degrees C for 50 h. The weight loss of all the coated samples was less than that of the uncoated Si3N4 with CMZP-coated samples exhibiting the smallest weight loss. There was no decrease in the flexural strength of Si3N4 after coating with zirconia and CMZP, and a decrease in strength after coating with either mullite or alumina. After alkali exposure, the strength of the CMZP and zirconia coated samples were significantly higher than those of the mullite-coated, alumina-coated, and uncoated Si3N4. The observed behaviour is explained in terms of the microstructure and protection mechanisms.