At temperature above 1200°C, the thermal stability of α-SiAlON phases has been debated since 1992; however, it has been discussed if any α-SiAlON phase can be formed in Ce, La, Eu and Sr-doped SiAlON systems. In our previous studies it was shown that the use of Mg-Ce and Mg-Sr elements as dopants SiAlON compositions, in which all elements just have very low or no stability in the α-SiAlON structure, would promote the stability of Mg-Ce elements in the α- SiAlON phase [1, 2]. However, in Mg-Sr systems, it was obtained that Mg2+ is predominantly incorporated in α-SiAlON structure whereas Sr2+ mainly remains in the grain boundaries . In this study, by applying spark plasma sintering (SPS) (at 1400-1700°C) and post-sintering thermal heat treatment (at 1500°C for 5 hrs and 1700°C for 2hrs) Mg or Mg-Sr doped SiAlON (50:50 mole ratios) ceramics were prepared. The results were compared with GPS sintered samples data. The effect of sintering temperature on densification process, phase transformation, microstructure and mechanical properties of samples were investigated. The results showed that by using SPS, Sr-Mg doped samples can be sintered at lower temperature (at 1600°C) than at GPS (at 1800°C) and it has no Sr-doped grain boundary phases.