The　ultrafine　WC-12Co　composite　powder　was　synthesized　by　in　situ　reduction　and　carbonization　reactions.　Using　the　composite　powder　with　an　addition　of　1.0wt%　grain　growth　inhibitor　(GGI)　i.e.　VC,　Cr3C2　and　NbC,　as　raw　materials,　the　ultrafine-structured　cemented　carbide　coatings　were　fabricated　by　the　high　velocity　oxy-fuel　(HVOF)　spraying　method.　Prior　to　thermal　spraying,　the　powders　were　agglomerated　into　thermal　spray　feedstock.　The　effects　of　GGI　addition　on　phase　constitution,　microstructure,　hardness,　and　wear　and　corrosion　properties　of　the　coatings　were　investigated.　The　results　show　that　the　mean　WC　particle　size　of　coatings　with　an　addition　of　1.0wt%　VC　or　Cr3C2　decreases　by　about　49%　as　compared　to　that　without　GGI.　Moreover,　hardness　of　the　coatings　is　significantly　improved　and　the　wear　rate　decreases　by　52%-55%.　Addition　of　1.0wt%　NbC　has　little　effect　on　WC　particle　size　of　the　coating　but　leads　to　formation　of　(W,　Nb)　C　compound　in　the　Co　binder.　Thus　the　corrosion　resistance　of　the　coating　containing　NbC　is　significantly　enhanced.　However,　its　wear　resistance　is　lower　than　those　with　VC　or　Cr3C2,　due　to　high　brittleness　of　the　(W,　Nb)　C　compound.