*Result*: Enhancing Mechanical Performances of Material Extrusion Additively Manufactured Composite Sandwich Structures via Multi‐Scale Interfacial Bonding Strategies.

*Material extrusion additive manufacturing demonstrates considerable potential in fabricating core structures with complex and advanced geometries, which greatly promotes the mechanical performances of sandwich composites. However, the interfacial bonding limitations between the core and skin sheets restrict the promised superior mechanical properties of the overall sandwich composites. This study addresses the weak interface bonding issue by innovatively combining meso‐grooves with sub‐micro GNP addition to form a multi‐scale enhancement strategy. Measured data from the three‐point bending tests revealed that these modifications resulted in a 28% increase in bending strength and a 59.2% increase in bending modulus compared to untreated composite sandwich structures. Scanning electron microscopy (SEM) and schematic illustrations further explained the underlying mechanisms contributing to the improved interfacial strength. During the fused deposition modeling process, the meso‐grooves were created onto the top surfaces of the short‐carbon fiber‐filled ABS (CF‐ABS) core, establishing mechanical interlocking textures for the continuous‐carbon fiber fabric skin. Controlled alignment of chopped fibers extending beyond deposited bead boundaries created microscale interfacial connections between the epoxy resin matrix and the core/skin laminates. Additionally, the graphene nanoplatelets (GNP) were integrated into the epoxy resin to achieve sub‐microscale reinforcement via interfacial bridging effects. The meso‐grooves amplified the interfacial contact area through mechanical interlocking, while the addition of GNP‐optimized resin‐fiber interfacial stress transfer. [ABSTRACT FROM AUTHOR]*