The oxidation behavior of multi-cation alpha-Sialons containing Nd and Y or Yb has been investigated for the compositions (Nd0.18Y0.18)Si10.38Al1.62O0.54N15.46 and (Nd0.18Yb0.18)Si10.38Al1.62O0.54N15.46 respectively in the temperature range of 1200degreesC to 1400degreesC in air. The grains of silicate containing Nd and Y as well as Nd and Yb were observed in preferred orientation on the surface of the materials oxidized at 1200degreesC or 1300degreesC for 20 h for (Nd,Y)- and (Nd,Yb)-alpha-Sialon respectively. By increase of oxidation temperature from 1300degreesC to 1400degreesC, bubble, which was caused by softening of silicate oxidation layer, occurred and glassy phase then appeared obviously. The phases formed on the surfaces of multi-cation alpha-Sialons during the oxidation were also discussed in this paper.