Global warming and the depletion of fossil resources have become crucial problems. One important way to address these problems is through the replacement of fossil resources with “sustainable” biomass resources, which has been investigated in this research. Cellulose is one of the most abundant biomass resources on earth and it has lower density (1.5 g/cm3) than other inorganic filler. Additionally, the cellulose as the wood-based biomass does not compete against food production. There is a fact that there is a large amount of biomass which is not yet used efficiently in Japan. For this reason, there is a great need to develop ways to effectively utilize and benefit from this enormous supply. So we developed to find effective use of cellulose: the flake-shaped cellulose particles (FSCP). The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. As a result, these have a flat shape like talc and mica. Therefore, we can expect to improve vibration-damping and gas barrier properties of the composite including the FSCP. In this study, as the biomass material, the green composite based on natural rubber (NR) and FSCP was produced. Vulcanizing agents of the rubber composite are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The FSCP and NR were mixed with the vulcanizing agents in an internal mixer. The functionalities of the composites were evaluated by a vibration-damping test and a gas permeability test. And functionalities of the composite including the FSCP was compared to the composite with talc or mica. Moreover, the shape, size and orientation of fillers within the composites were observed.