The present invention relates to biomass resin composition comprising a phenolized biomass substance and a reactive substance having a melting point of at most 100.degree. C. other than phenol. The biomass resin composition is prepared by a process, which comprises adding a reactive substance such as a phenol derivative or drying oil into the reaction system, in the step of preparing a phenolized biomass substance by phenolizing a biomass substance with a phenol in the presence of an acid catalyst. The present invention provides a biomass resin composition, in which the melting point can be freely controlled and which is excellent in properties such as flowability, processability, water resistance and impact resistance and can be prepared by a simple process, and a process for preparing the same.