Ultracoarse　grained　WC-Co　cemented　carbides　are　widely　used　as　tool　materials　for　service　under　extreme　conditions.　Their　working　life　is　affected　greatly　by　the　toughness　and　the　deformation　mechanisms.　In　this　work,　ultracoarse　grained　cemented　carbides　were　prepared　by　sintering　the　mixture　of　Co　and　coarse　WC　powders.　Using　the　designed　samples,　the　indentation　induced　deformation　was　obtained　by　a　Vickers　hardness　tester　with　a　load　of　30kg.　The　scanning　electron　microscopy　and　electron　backscatter　diffraction　were　used　to　study　the　microstructure　morphology　and　WC　crystal　orientations.　The　hardness　and　elastic　modulus　of　the　single　WC　crystal　in　the　deformed　zone　were　measured　by　the　nanoindentation.　This　study　proposes　that　slipping　in　the　WC　grains　play　a　significant　role　in　the　deformation　behaviour　and　the　toughness　of　the　ultracoarse　grained　cemented　carbides.