PURPOSE: To produce a lignin graft copolymer made of a lignin-containing material, i.e., lignin, grafted wood, grafted wood fiber, or grafted pulp, by preparing an environment free of O2 and forming a reaction mixture made up of a lignin-containing material, a redox initiator, a halogenated salt, and a specified monomer followed by polymerization.

CONSTITUTION: An environment free of O2 (e.g. an environment of N2) is prepared and a reaction monomer made up of a lignin-containing material, a redox initiator (e.g. H2O2), a halogenated salt (e.g. CaCl2), and a monomer represented by formula I and/or II (wherein R1-2 each represent an organic functional group that does not interfere with the polymerization reaction) is formed and is polymerized.