A method for producing a PC copolymer with improved productivity is provided. The PC copolymer has a specific structure and the method uses a diester diol-containing monomer as a raw material. The polycarbonate copolymer is produced by reacting a diester diol-containing monomer, a divalent phenol, and a carbonate precursor by interfacial polymerization, wherein the diester diol-containing monomer is a product of reaction between a hydroxybenzoic acid or an esterified product thereof and a polyalkylene glycol, wherein the esterification degree of hydroxyl groups of the polyalkylene glycol is 50 to 90 mol %.