In　this　work,　the　effects　of　composition,　carbide　grain　size,　and　WC　matrix　structure　on　the　mechanical　properties　of　low-density　WC-TiC-Co　cemented　carbides　have　been　studied.　It　is　found　that　increasing　the　TiC　content　promotes　WC　dissolution　into　TiC　to　form　a　(Ti,W)C　solid　solution.　When　the　TiC　particle　size　exceeds　approximate　to　2　mu　m,　the　sintered　alloys　exhibit　a　mixed　microstructure　of　(Ti,W)C　and　core-shell-structured　(Ti,W)C@TiC　grains.　Refining　TiC　to　the　ultrafine　scale　eliminates　the　core-shell　structures　and　generates　a　transition　layer　between　WC　and　(Ti,W)C　phases.　This　transition　layer　forms　coherent　and　semi-coherent　interfaces　with　the　adjacent　carbides　through　lattice　distortion　and　dislocation　accommodation,　which　enhances　interfacial　bonding　and　increases　intergranular　fracture　resistance.　Furthermore,　by　incorporating　ultrafine　WC-Co　composite　powder　to　partially　replace　submicron　WC,　a　bimodal　grain　microstructure　is　obtained　in　the　sintered　alloy,　along　with　the　formation　of　numerous　Co-rich　nanoparticles　within　WC　grains.　The　prepared　WC-TiC-Co　cemented　carbides　with　optimized　TiC　content　and　particle　size　achieve　reduced　density　and　enhanced　mechanical　properties　simultaneously.　The　present　findings　provide　new　insights　into　strengthening　and　toughening　of　low-density　cemented　carbide　materials.