The wear characteristics of plasma spray coated layer of Alumina-Titaina composite powder have been investigated, in this study, focusing on the effect of particle size of Alumina powder and parameters of plasma spray coating process. Alumina-Titania composite powders were artificially agglomerated into the size suitable for plasma spray coating process. The process condition for plasma spray coating has been optimized through a statistical data treatment method i.e. response surface analysis. Mechanical properties of coated layer have been measured as a function of the initial Alumina particle size. The structure of Alumina nano-powders in the coated layer was found to be affected by flow rates of Ar and H2 gases, and the power of plasma in a combinational way. The relationship between the wear characteristics of coated layer and process parameters and microstructure of the coated layer was elucidated, by measuring the size distribution, temperature, and velocity of traveling Alumina-Titania composite powder agglomerates. Abstract only; no full-text paper available.