Studies on lattice structures fabricated by material extrusion additive manufacturing for metal, leveraging the advantages of additive manufacturing, are limited. In this work, by varying the number of unit cells, the effects of density on the macro- and microstructure, and on the physical and mechanical properties of 316L stainless steel fabricated by our in-house developed 316L metal-filled filament were investigated. Utilising our in-house developed 316L metal-filled filament, supportless octet-truss lattice specimens with relative density ranging from 16 % to 55 % were successfully fabricated. The relative density increased with the number of unit cells, compressive strength, Young's modulus, and energy absorption, consistent with the Gibson-Ashby's porous material model. Stretch-dominated behaviour was observed in the 2 × 2 × 2 and 3 × 3 × 3 unit cells, while the 4 × 4 × 4 and 5 × 5 × 5 units exhibited bending-dominated behaviour. The deformation behaviour was well simulated by finite element analysis with the core-shell structure. The successful fabrication of supportless lattice structures highlights their potential for manufacturing lightweight materials and their future application.