To obtain molded articles by uniformly and efficiently graft polymerizing an ethylenically unsaturated organic acid onto hydrophobic polymer molded articles without causing hang-up of by-produced polymers.

In the process for the graft polymerization processing of hydrophobic polymer molded articles free from the hang-up of by-produced polymers by dipping the hydrophobic polymer molded articles in an aqueous emulsion containing a hydrophobic radical initiator, an N-alkylphthalamide compound, and an ethylenically unsaturated organic acid, and heating the articles thus treated, the aqueous emulsion whose pH at room temperature is adjusted to 2.5-3.5 with an alkali metal compound is used. Graft polymerization processed articles can be obtained by this process.