PROBLEM TO BE SOLVED: To provide a polymer electrolyte exhibiting excellent proton conductivity.SOLUTION: A polymer electrolyte includes sulfonic acid group-containing polyimide having a repeating unit represented by formula (1). When infrared spectroscopic analysis is performed to each surface of the polymer electrolyte measured from three directions of a first direction, a second direction and a third direction intersecting orthogonally with each other, an absorbance ratio (D/D) between a maximum absorbance (D) at 1,340-1,360 cmand a maximum absorbance (D) at 1,650-1,690 cmof an infrared absorption spectrum measured in each direction is calculated, and the minimum value and the maximum value among the calculated three absorbance ratios (D/D) are selected, a ratio (maximum value/minimum value) of both values is 2.0 or more.
