Lignin xanthate was used as chain transfer agent for the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide (AM). The lignin-g-PAM-CTA was employed for the preparation of lignin-g-PAM-b-PMMA block copolymer by adding the second monomer methyl methacrylate (MMA). The successful formation of block copolymers was confirmed by FT-IR, 1H-NMR, GPC, DSC and TGA. The lignin-g-PAM-b-PMMA block copolymer possesses a higher molecular weight and a wider molecular weight distribution. The temperature of the initial decomposition or maximum mass loss for the lignin-g-PAM-b-PMMA block copolymer is significantly increased, while the glass transition temperature exists between that of lignin-g-PAM and PMMA.