PURPOSE: To efficiently obtain the subject product of good quality in which a desired amount of a polymer is held in intracellular cavities without using an organic solvent by holding a polymer raw material in a specific state in the intracellular cavities of a lignocellulosic material, polymerizing the raw material and pulping the aforementioned material.

CONSTITUTION: A dispersion composed of a polymer raw material selected from polymerizable monomers and oligomers thereof and a dispersant containing water is initially injected into intracellular cavities of an unfiberized lignocellulosic material (preferably wood chips) and held therein. The aforementioned polymer raw material is then polymerized and immobilized in the above-mentioned intracellular cavities. The resultant unfiberized lignocellulosic material holding the polymer is subsequently pulped to afford the objective product. Furthermore, vinylic monomers, such as styrene, are preferred as the polymer raw material. The dispersion containing the polymer raw material is preferably prepared by a method for using an aqueous medium containing a surfactant.