Gas　permeation　behaviour　through　atmospheric　plasma-sprayed　8　mol%　yttria　stabilized　zirconia　(YSZ)　electrolyte　coating　was　studied　experimentally.　YSZ　coatings　were　fabricated　using　different　powder　feedstock.　The　temperature　and　velocity　of　in-flight　particles　during　spraying　were　measured　with　a　diagnostic　system.　The　results　showed　that　particle　temperature　and　velocity　were　significantly　influenced　by　the　size　of　powders.　The　gas　permeability　of　these　coatings　was　estimated　by　a　specific　instrument　with　pure　O-2,　N-2　and　H-2.　It　was　found　that　the　gas　permeability　was　reduced　by　decreasing　the　size　of　powder.　Gas　permeation　behaviour　through　plasma-sprayed　YSZ　coating　was　studied.　Transition　flow　was　compatible　to　gas　permeation　behaviour　for　all　three　plasma-sprayed　YSZ　coatings.　The　relationship　between　gas　permeation　behaviour　and　coating　microstructure　is　discussed　in　this　article.　(c)　2008　Elsevier　B.V.　All　rights　reserved.