Provided are an electrode catalyst layer, a membrane electrode assembly and a polymer electrolyte fuel cell, having sufficient drainage property and gas diffusibility with high power generation performance over a long term. An electrode catalyst layer (10) bonded to a surface of a polymer electrolyte membrane (11) includes at least a catalyst substance (12), a conductive carrier (13), a polymer electrolyte (14) and fibrous substances (15). The number of the fibrous substances (15) in which inclination θ of axes with respect to a surface of the electrode catalyst layer (10) bonded to the surface of the polymer electrolyte membrane (11) is 0°≤θ