An advantage of alpha-SiAlON is that it can accommodate cations of sintering additives and hence reduces the amount of deleterious remnant intergranular amorphous phase. However, it is believed that relatively large cations cannot enter the structure. In this work, TEM-EDX combination is used to find out whether large cations of Sr2+. can be incorporated into the alpha-SiAlON structure. The results showed that Sr2+ can enter the structure if other smaller cations of Ca2+ or Yb3+ are also present.