Banana fiber is a natural, biodegradable fiber from banana plants which is popular for its better strength, biodegradability, eco-friendly, and it is light weight. Flax is also a natural fiber which is also appreciated for its strength, durability, and eco-friendly. Both fiber-reinforced composites become better alternative material in automotive, aerospace, and construction industries. This work was concentrated on the natural epoxy composites made with combined banana and flax reinforcement and epoxy resins. The composite plates have fabricated using hand lay-up method processing method with dimensions of 200 mm × 200 mm × 3 mm. The plates are stacked in the following patterns: [0F/0F/0F/0F], [0B/0B/0B/0B], [0F/0B/0F/0B], [0F/90B/90F/0B], [0F/90B/90B/0F], and [0B/90F/0B/90F], where F represents flax fiber and B represents banana fiber. The three types of nanopowder synthesized and mixed with epoxy resin, the same six plates were fabricated. To characterize the hybrid composites, tensile test, flexural tests, and Izod impact test were performed. For composite plates with nanoparticles, tensile testing revealed maximum longitudinal 132 MPa and transverse tensile strength of 142 MPa. Similarly, flexural testing demonstrated a flexural strength of 505.3 MPa and exhibited an impact strength of 160.2 kJ/m2 highlighting its resistance to bending. For hybrid composites without nanoparticles exhibited the strength values far below the strength values of nanoparticle composite plates. Overall, the banana–flax–epoxy composite was identified as alternative material for car door trims due to its promising mechanical properties. These combined properties make the banana–flax–epoxy composite a suitable and sustainable choice for car door trims.