A new and simple chemical route, named microwave-induced poly(vinyl alcohol) (PVA) solution polymerization, has been used to prepare fine, homogeneous and high-density pellets of purer La0.8Sr0.2Ga0.83Mg0.17O2.815 (denoted as LS0.2GM0.17). The effect of different contents of PVA as the polymeric carrier, was studied and we obtained an optimal amount of PVA (1.65:1 ratio of positively charged valences of the cations (Men+) to negatively charged hydroxyl (–OH−) groups of the organics), which could ensure homogenous distribution of the metal ions in the polymeric network structure and inhibit segregation. The behavior of the powder after calcination at different temperatures was studied. The PVA solution process consumed less organic material compared with the Pechini process, and consequently PVA was a more effective carrier in the preparation of LSGM. Higher heating rate and a more homogenous heating manner without thermal gradients in the microwave oven resulted in fewer secondary phases in the LS0.2GM0.17 powder after calcination at 1400 °C for 9 h and a smaller pellet grain size (2–3 μm) without segregation. The density of LS0.2GM0.17 pellet sintered at 1400 °C for 9 h was 6.19 g cm−3.