Powder loading effects have been reexamined for various yttria-stabilized zirconia powders under atmospheric dc plasma spraying. A laser illumination method was utilized to observe powder injection into the plasma jet, while single particle and ensemble methods to measure particle state parameters. Statistical temperature distributions of in-flight particles suggested a rapid increase in the number of semi-molten particles above a certain powder loading rate. Despite drops in the particle temperature and velocity due to the powder loading effect, the deposition efficiency tends to have increased in some cases. Reliability of the single particle and ensemble methods has also been examined at various powder feed rates. Particle temperature measurement by the ensemble method at low powder feed rates could cause a significant error, which may affect powder injection optimization. Particle plume trajectory was not affected as much by the powder loading, which hence had only a limited effect on the particle diagnostics.