For the purpose of developing new engineering materials based on inedible plant-derived materials, we investigate the dynamic viscoelastic properties of ternary biomass composites (hemp fiber (HF)/ plant-derived polyamide 1010 (PA1010)/ maleic anhydride grafted polypropylene (PP-g-MA)) in molten state. PA1010 was made from sebacic acid and decamethylenediamine, which are obtained from plant-derived castor oil. HF, which is one of the natural fibers, was used as a reinforcement fiber. HF was surface-treated by two types of surface treatment: (a) alkaline treatment by sodium chloride (NaClO2) solution and (b) surface treatment by ureidosilane coupling agents (A-1160). PP-g-MA (2wt.%) was used as a compatibilizer. These ternary biomass composites were extruded using a twin extruder, and compression-molded. Dynamic viscoelastic properties in the molten state were evaluated by oscillatory flow testing using a parallel plate-type rotational rheometer. It was found that addition of PP-g-MA and surface treatment of HF have stronger influence on the dynamic viscoelastic properties of the biomass composites in molten state. These may be attributed to the change in the internal microstructure formation such as fiber network formation, fiber dispersion and interfacial interaction between HF and PA1010.