Provided are an electrode catalyst layer for a polymer electrolyte fuel cell, which is capable of improving drainage property and gas diffusion properties and capable of high output, and a polymer electrolyte fuel cell provided with the same. An electrode catalyst layer (2, 3) bonded to a polymer electrolyte membrane (1) includes a catalyst (13), carbon particles (14), a polymer electrolyte (15) and fibrous material (16), in which the electrode catalyst layer (2,3) has a density falling within a range of 500 mg/cm3 to 900 mg/cm3, or has a density falling within a range of 400 mg/cm3 to 1000 mg/cm3, and the mass of the polymer electrolyte (15) falls within a range of 10 mass % to 200 mass % with respect to the total mass of the carbon particles (14) and the fibrous material (16).