The growing demand for environmentally friendly composite materials that utilize natural resources as reinforcement has driven efforts to reduce dependence on synthetic fibers. Sansevieria trifasciata fiber and Leucaena leucocephala wood powder have potential as reinforcement and filler in composites with a synthetic Styrene Butadiene Rubber (SBR) latex matrix, owing to their high cellulose content and abundant availability in Indonesia. This study aims to determine the effect of composition variation of sansevieria fiber and lamtoro wood powder on the bending strength and to identify the macro structure of the resulting composite. The composition variation was designed using a mixture Design of Experiments (DOE), producing 13 composition variations, five of which were center points used as controls. Specimens were fabricated using the hand lay-up method following the ASTM D790 standard, then tested using a Universal Testing Machine, with macro structure observation performed on the fracture surfaces. The results showed that the highest flexural stress of 13.10 MPa was obtained at a composition of 24.90% sansevieria fiber, 28.00% lamtoro wood powder, and 47.10% SBR latex, while the lowest value of 5.98 MPa was obtained at 5.10% fiber, 28.00% wood powder, and 66.90% SBR latex. The highest modulus of elasticity was 754 MPa and the lowest was 368 MPa. Macro structure observation indicated that a more homogeneous distribution of fiber and filler along with better interfacial bonding contributed to higher bending strength. Variation in the composition of the constituent materials was proven to significantly affect the mechanical properties of the composite, with sansevieria fiber acting as the primary reinforcement and lamtoro wood powder as the filler.