AbstractWithout using fossil resources such as petroleum and coal, which are likely to be depleted and have a large load on the environment, we studied the improvement of the performance of phenolic resin using lignin‐based natural material, which is a non‐fossil resource that is less likely to cause environmental problems. Using modified lignin with polyethylene glycol, the modified lignin phenolic novolac resin was synthesized, and the properties of the phenolic resin molding material and molded article containing the modified lignin were evaluated. As a result, it was found that the phenolic resin into which the modified lignin was introduced not only has excellent moldability, but also excellent heat resistance, mechanical strength, and electrical insulation, and can achieve both heat resistance and flexibility.