The aim of this study is to investigate the Influence of initial fiber length on the mechanical properties of hemp fiber filled plants-derived polyamide 1010 biomass composites in order to develop the new engineering materials such as structural materials and tribomaterials based on all plants-derived materials. Plants-derived polyamide 1010 (PA1010) was made from plant-derived castor oil. Hemp fiber (HF) was previously cut into length of 5mm, 10mm, 20mm and 50mm, and was surface-treated by two types of treatment: alkali treatment by NaOH solution and surface treatment by ureido silane coupling agent (HF-S). The volume fraction of HF-S in the composites was fixed with 20vol.%. HF-S/PA1010 biomass composites were extruded by a twin screw extruder and injection-molded. Their mechanical properties such as tensile, bending, Izod impact and Durometer hardness, and tribological properties by ring-on-plate type sliding wear testing were evaluated. It was found that the mechanical properties of HF-S/PA1010 biomass composites change with the initial fiber length of HF. The critical fiber lengths of various mechanical properties of these biomass composites decrease as follows: strength > modulus > elongation at break > Izod impact strength. Tribological properties such as frictional coefficient and specific wear rate also change with the initial fiber length. The frictional coefficient of these biomass composites slightly decrease with increasing the fiber length. On the other hand, the specific wear rate of these biomass composites dramatically improved with increasing the fiber length, and has a minimum peak at 20mm. It follows from these results that it may be possible to develop the new higher performance engineering materials by selecting the suitable fiber length.