This paper describes the oxidation behaviour of Si 3 N 4 /Y 2 O 3 -based ceramics. We prepared three kinds of ceramics, which have excellent crack-healing abilities, in different composites – Si 3 N 4 /Y 2 O 3 , Si 3 N 4 /SiC/Y 2 O 3 , and Si 3 N 4 /Y 2 O 3 /Al 2 O 3 – and investigated the effect of crack-healing treatment on their oxidation behaviour. The oxidation tests were carried out at 700–1200°C for 500h. Measurements of weight gain and bending strength and observations of the oxidized surfaces were carried out.The main results obtained are as follows: (1) when Y 2 O 3 was used as an additive, Si 3 N 4 ceramics exhibited extensive oxidation at low temperatures (700–1000°C). (2) Si 3 N 4 /Y 2 O 3 ceramics with 3-wt% Al 2 O 3 added as an additive showed no extensive oxidation. (3) Crack-healing, as a pre-oxidation treatment, is useful for increasing the oxidation–resistance of ceramics at 1000°C and for increasing the strength.