Er:Al2O3 powders were synthesized by co-precipitation and sintered using either traditional pressure-less sintering or microwave sintering. By utilizing two different types of microwave sintering, multi-mode and single-mode, the effect of different types of microwave fields on the sintering behavior of Er:Al2O3 was studied. Using single-mode microwave sintering, the percentages of electric and magnetic fields that the sample was exposed to during sintering was varied by adjusting the position of the sample along the processing microwave cavity. This experimental parameter has not been widely explored in microwave sintering, and may provide new insight into how the different fields affect a variety of processes throughout the sintering process. Our preliminary results suggest that this may be the case. Overall, the microwave sintering parameters appear to have a profound influence on the densification and, possibly, RE migration/phase stability. Sintering in the single-mode microwave system, with a 30%E:70%H mixed field produced samples with significantly higher density (∼97% of theoretical of alumina) than all of the other samples sintered at 1400°C (and equal to the sample conventionally sintered at 1700°C). This high density represents a significant improvement over the conventionally-sintered (1400°C) sample, which had a density ∼70% of the theoretical density. Whether due to the higher density or a microwave effect in itself, this sample also contained the least amount of second phase, which indicated that more Er formed a solid solution with Al2O3. While our results indicated mat densification and Er stability within the lattice may both improve with increasing magnetic field, our data is too limited to form a concrete conclusion. Regardless, our findings suggest that the magnetic component may play a critical, if not well understood, role in the processing of weakly magnetic materials such as Al2O3, and that the dopant material (RE in this case) may play an important role to the material response to the EM fields.