<p>Coarse-grained WC-10Co cemented carbides are indispensable for demanding applications such as rock drilling and shield tunneling, yet their development is restricted by poor mixing uniformity and the inherent hardness-toughness trade-off. To address this issue, a series of coarse-grained WC-10Co cemented carbides was developed by systematically tuning the ratios of La₂O₃ and Y₂O₃ additives via a co-precipitation and hydrogen reduction. The microstructures and mechanical properties were highly sensitive to this ratio. The optimal balance was achieved at a La: Y atomic ratio of 1:2, yielding a hardness of 86.6 HRA, a bending strength of 2201 MPa, and a remarkable fracture toughness of 25.72 MPa·m^1/2. This improvement is mainly attributed to a synergistic interface-pinning mechanism. Specifically, trapezoidal La₂O₃ and spherical Y₂O₃ particles preferentially segregate at the WC/Co phase boundaries, thereby inhibiting abnormal WC grain growth and suppressing the martensitic transformation of ductile face-centered cubic cobalt (Co_FCC). Consequently, optimizing the additive ratio effectively alleviated the hardness-toughness trade-off, providing an effective paradigm for tailoring high-performance cemented carbides through precise powder-mixing engineering.</p>