Pores　are　common　defects　in　the　coating　formed　via　plasma　spraying.　In　order　to　investigate　the　formed　mechanism　of　pores　in　plasma　sprayed　nanostructured　Al2O3-TiO2　coatings,　the　microstructure　of　the　feed　stock,　splat　and　coating　were　characterized　by　means　of　scanning　electron　microscopy　(SEM).　The　coating　shows　a　typical　lamellar　morphology,　which　contains　fully　melted　(FM)　zone　and　partly　melted　(PM)　zone.The　pores　in　different　places　of　the　coating　were　generated　from　different　sources.　The　shapes　and　the　size　of　the　pores　are　also　different.