In order to enhance thermal properties of biomass plastics, i.e., plastics made from plant biomasses, modification of backbone structure and processing conditions have been attempted. As the modification of backbone structure, utilization of cinnamic acid derivatives in the polyester was found effective to enhance the glass transition and degradation temperatures. In particular, utilization of ferulic acid led to express liquid crystalline nature. As the modification of processing conditions, utilization of polysaccharide derivatives as the nucleating agent of poly(lactide) stereocomplex was attempted. As the result, enhanced stereocomplex formation without homocrystal formation after the isothermal crystallization below the melting point of homocrystal was attained.