A membrane electrode assembly for use in a polymer electrolyte fuel cell, comprising: a polyelectrolyte membrane having a first surface and a second surface facing away from the first surface; a fuel-electrode-side electrocatalyst layer bonded to the first surface and containing a first catalytic material, a first electrically conductive carrier, and a first polyelectrolyte, the first electrically conductive carrier carrying the first catalytic material; and an oxygen-electrode-side electrocatalyst layer bonded to the second surface and containing a second catalytic material, a second electrically conductive carrier, a second polyelectrolyte, and a fibrous material, the second electrically conductive carrier carrying the second catalytic material, wherein, the membrane electrode assembly contains voids, the voids including pores each having a size in a range of 3 nm or more and 5.5 μm or less, a distribution curve indicating distribution of pore volume with respect to pore size has a peak at which the pore size is in a range of 0.06 μm or more and 0.11 μm or less, the pore volume being a sum of volumes of pores having a specific pore size among the pores and being measured by mercury intrusion porosimetry under the conditions described in paragraphs and of EP 3 780 192 A1, the pore size being a diameter of a pore calculated from the pore volume according to the method described in paragraphs to of EP 3 780 192 A1, and a percentage of an integrated pore volume to a geometric volume is in a range of 60% or more and 80% or less, the integrated pore volume being obtained by integrating the pore volumes of the pores having pore sizes in the range of the pore size, the geometric volume being obtained by subtracting a geometric volume of the polyelectrolyte membrane from a geometric volume of the membrane electrode assembly. a polyelectrolyte membrane having a first surface and a second surface facing away from the first surface; a fuel-electrode-side electrocatalyst layer bonded to the first surface and containing a first catalytic material, a first electrically conductive carrier, and a first polyelectrolyte, the first electrically conductive carrier carrying the first catalytic material; and an oxygen-electrode-side electrocatalyst layer bonded to the second surface and containing a second catalytic material, a second electrically conductive carrier, a second polyelectrolyte, and a fibrous material, the second electrically conductive carrier carrying the second catalytic material, wherein, the membrane electrode assembly contains voids, the voids including pores each having a size in a range of 3 nm or more and 5.5 μm or less, a distribution curve indicating distribution of pore volume with respect to pore size has a peak at which the pore size is in a range of 0.06 μm or more and 0.11 μm or less, the pore volume being a sum of volumes of pores having a specific pore size among the pores and being measured by mercury intrusion porosimetry under the conditions described in paragraphs and of EP 3 780 192 A1, the pore size being a diameter of a pore calculated from the pore volume according to the method described in paragraphs to of EP 3 780 192 A1, and a percentage of an integrated pore volume to a geometric volume is in a range of 60% or more and 80% or less, the integrated pore volume being obtained by integrating the pore volumes of the pores having pore sizes in the range of the pore size, the geometric volume being obtained by subtracting a geometric volume of the polyelectrolyte membrane from a geometric volume of the membrane electrode assembly. <EOS>