Abstract: Nano-Al2O3 coatings with low dielectric constants were fabricated via suspension plasma spraying two powders of α-Al2O3 and γ-Al2O3, and they were compared with conventional atmospheric plasma spraying nano-agglomerated Al2O3 coatings. The effects of spraying method on the phase composition, microstructure, hardness, porosity and dielectric constant were studied. The results show that the final phase composition of the coatings is greatly affected by the powder phase composition and the spraying method. The coating prepared by γ agglomerated powders has more γ phases, which is 48.8%, the coating prepared by suspension plasma spraying α phase powders has the highest α phase content, which is 98.5%, and the coating prepared by suspension plasma spraying γ phase powders has a γ phase content of 34.4%. It shows that the suspension spraying process can significantly reduce the amount of powder in the plasma and inhibit the preferential nucleation of the γ phase. There is no obvious boundary between the fully molten area and the semi-molten area in the suspension coating microstructure, no obvious layered structure and crack in the fracture section, and the hardness dispersion of the molten area of the suspension plasma coating is smaller. The coating prepared by suspension plasma spraying γ phase powders has the lowest relative dielectric constant, which is about 5.96 F/m. The powders are heated more evenly during suspension plasma spraying, which can reduce the preferential nucleation of the γ phase and improve the microstructure and hardness distribution uniformity of the coating. The coating microstructure is the primary influencing factor on the dielectric constant of the suspension plasma coating.