The results presented in this paper compare the behavior of silicon nitride prepared with the addition of yttria as sintering additive, and of a sialon ceramic in contact with an aqueous solution of sodium chloride (NaCl) at T <= 290 degrees C. Both studied ceramics dissolved by preferential attack of Si-N bonds in the matrix accompanied by the release of ammonia and formation of protective, mostly oxide layer of corrosion products at the surface. Increase of dissolution rate of sialon in aqueous NaCl solution at 290 degrees C was observed in comparison to dissolution in deionized water, achieving the value 27 mmol.(m(2).h) (1). Penetration of chloride anions through protective layer of corrosion products is proposed to contribute to destruction of the passivation layer and renewal of the exposure of vulnerable material surface to corrosion medium.