As a biodegradable polymer completely derived from renewable resources, polylactide (PLA) exhibits a great potential to widely replace traditional petroleum-based polymers because of its excellent transparency and good mechanical strength, etc. However, its applications have been hindered by its inherent brittlement and low toughness. Blending PLA and elastomer is a practical and economic way to modify the brittlement, but a substantial elastomer concentration of 15-20 wt% is required, which in turn leads to a considerable loss in the strength and stiffness. Therefore, in order to achieve good stiffness-toughness balance, much attention has been paid to increasing the toughening efficiency in recent years. In this work, taken PLA/poly(ether)urethane (PU) (85/15) blend as an example, hydrophilic silica (SiO2) nanoparticles with self-networking capability were used to control the phase morphology and the resulting mechanical properties. Very interestingly, the results shows that the introduction of SiO2 nanoparticles in the blend melt induces the morphological change from a common sea-island structure to a unique network-like structure constructed by discrete PU particles, thus giving rise to a remarkable improvement in the toughening efficiency with strength and modulus unaffected. The formation of the network-like structure is mainly ascribed to the self-networking of the interface-localized SiO2. This work could provide a universal platform for optimizing the comprehensive performance of polymer blends via nanoparticles-assisted design of phase structure.