A block copolymer, an ion-exchange membrane including the block copolymer and a method of preparing the block copolymer are provided. It relates to a block copolymer comprising a hydrophobic repeatingunit represented by the following Chemical Formula 1 and a hydrophilic repeating unit represented by the following Chemical Formula 2, the ion-exchange membrane including the same, and the method ofproducing the same. The present invention can provide a chain extender to introduce a chain, can increase the molecular weight of a polymer, can ensure excellent mechanical properties and long-term stability, and introduce a phenylene structure into a block copolymer that ensures chemical stability, and can improve electrochemical performance.