Abstract: Provided are a sulfonated poly(arylene ether) copolymer including a crosslinking structure and a polyelectrolyte membrane including the same. Particularly, a sulfonated poly(arylene ether) copolymer including a crosslinking structure in a polymer chain or at the terminal portion of the polymer chain, and a polyelectrolyte membrane including the same are provided. The polyelectrolyte membrane using the sulfonated poly(arylene ether) copolymer including the crosslinking structure, may have the same or better degree of a thermal stability, a mechanical stability, a chemical stability, a membrane forming capability, etc. than a commonly used polyelectrolyte membrane. In addition, the proton conductivity and the cell performance of the polyelectrolyte membrane may be remarkably improved than those of the commonly used polymer electrolyte. Further, the properties of the electrolyte membrane may be rarely changed, and a high measuring stability may be obtainable.