<p>Achieving simultaneously high strength and toughness in lightweight architected materials remains a fundamental challenge because of the inherent tradeoff between these properties. Herein, we propose a novel strategy for fabricating robust 3D lattice structures by integrating photopolymerization-induced phase separation with the formation of an interpenetrating phase composite (IPC). This approach enables the creation of bicontinuous nanostructures composed of a soft acrylate phase and a hard epoxy phase, which are uniformly distributed within a porous lattice fabricated via digital light processing 3D printing. The resulting soft–hard interface microstructures exhibit remarkable mechanical enhancements. Compared with those of solid structures with the same geometry, the compressive stiffness, strength, and toughness are improved by 35%, 12%, and 47%, respectively. In addition, these structures exhibit excellent fatigue resistance under cyclic loading due to efficient load transfer and energy dissipation through the multiscale bicontinuous network. This scalable and versatile platform not only overcomes the key limitations of traditional IPC fabrication methods but also opens new avenues for designing lightweight, damage-tolerant metamaterials. The proposed approach holds promise for diverse high-performance applications, including aerospace, biomedical, and protective systems.</p>