The hybrid composites of calcium carbonate powder (CaCO3) and kenaf natural fiber (Hisbiscus Canabinus) reinforced epoxy resin have been developed as an alternative material for the locomotive body platform application. The superiority of kenaf fiber such as high mechanical properties and renewable leads to potentially use for the natural fiber composite. Meanwhile, the advantages of epoxy resin as a matrix are easy to use, did not have the strong smell and able to stick to almost any surface. The differences of natural characteristic hydrophilic kenaf fiber and hydrophobic epoxy resin it is challenging to achieve bounding homogenous fibers in the matrix, this is an essential problem in the manufacture of natural fiber composite materials. Alkalization treatment is expected to overcome the kenaf/CaCO3/epoxyresin hybrid composite's deficiency, so that matrix and filler have a strong bond. This research aims to find out the effect of calcium carbonate (CaCO3) powder size towards mechanical properties (impact toughness) of the kenaf/CaCO3/epoxyresin hybrid composite. In this research, kenaf fibers were alkali treated in 6% NaOH for 4 hours. The alkali treated kenaf fiber 6 mm length and CaCO3 powder of various sizes (about 120 mesh, 200 mesh and 400 mesh) were used as fillers. The kenaf/CaCO3/epoxyresin hybrid composites were fabricated with a cold press machine by hand lay-up method. An impact test was carried out on all composite specimens according to ASTM D6110-04 standard. The fracture surface was characterized using a scanning electron microscope (SEM). Meanwhile, an optical microscope was used to characterize the fiber distribution in the matrix from a cross-section view. The results showed that kenaf/CaCO3/epoxyresin hybrid composite with 400 mesh has the highest impact toughness 0.00415 J/mm2. The smaller the size of CaCO3 particles the higher the impact toughness of the kenaf/CaCO3/epoxyresin hybrid composite.