The　grain-size　dependence　of　wear　resistance　of　WC-Co　cemented　carbides　(with　mean　WC　grain　sizes　of　2.2　mu　m,1.6　mu　m,　0.8　mu　m　and　0.4　mu　m,　respectively)　was　investigated　under　different　tribological　conditions.　The　results　showed　that　the　grain　size　had　opposite　effects　on　wear　resistance　of　the　cemented　carbides　in　dry　sliding　wear　and　microabrasion　tests.　In　the　former　condition,　with　decrease　of　WC　grain　size　hence　the　increase　of　hardness,　plastic　deformation,　fracture,　fragmentation　and　oxidation　were　all　mitigated,　leading　to　a　drastic　decrease　in　the　wear　rate.　In　the　latter　condition,　pull-out　of　WC　grains　after　Co　removal　dominated　the　wear,　so　that　the　hardness　of　cemented　carbide　was　not　a　core　factor.　As　a　result,　the　wear　resistance　of　the　cemented　carbide　generally　showed　a　decreasing　trend　with　decrease　of　the　grain　size,　except　for　a　slight　increase　in　the　ultrafine-grained　cemented　carbide.　Single-pass　scratching　of　the　cemented　carbides　under　various　loads　indicated　the　same　failure　mechanism　as　that　in　the　sliding　wear　tests.　Furthermore,　the　reasons　for　severe　surface　oxidation　of　the　coarse-grained　cemented　carbides　were　disclosed.　(C)　2019　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.