An electrode catalyst layer for a fuel cell, the electrode catalyst layer having a thickness T of 1 to 10 μm and comprising a catalyst-on-support having a particle size D of 10 to 100 nm and a hydrophilic material having a particle size d2 of 0.2 to 10 μm, the catalyst-on-support comprising a support which comprises an electroconductive inorganic oxide and a catalyst supported on the electroconductive inorganic oxide, the hydrophilic material being an agglomerate comprising hydrophilic electroconductive particles, the hydrophilic electroconductive particle having a particle size d1 of 10 to 100 nm, the hydrophilic material being present in an amount of 2 mass% or higher and lower than 20 mass% relative to the sum of the support and the hydrophilic material, the ratio of the particle size d1 to the particle size D being 0.5 to 3.0, the ratio of the particle size d2 to the thickness T being 0.1 to 1.2, wherein the catalyst comprises platinum; an alloy of platinum and a noble metal other than platinum; or an alloy of platinum and a base metal, wherein the hydrophilic electroconductive particles of the hydrophilic material and the support comprise at least one of an indium-based oxide, a tin-based oxide, a titanium-based oxide, a zirconium-based oxide, a selenium-based oxide, a tungsten-based oxide, a zinc-based oxide, a vanadium-based oxide, a tantalum-based oxide, a niobium-based oxide, and a rhenium-based oxide, wherein the particle sizes of the hydrophilic particle and the catalyst-on-support are determined by observing at a 100,000 times magnification in an electron micrograph a cross-section of a catalyst layer, by choosing the objects recognized as the smallest unit of a particle, judging from their apparent geometric form, by measuring the largest traverse length of 500 or more particles and calculating the average length, and wherein the particle size of the hydrophilic material is determined by observing at a 10,000 times magnification in an electron microscope a cross-section of a catalyst layer containing the hydrophilic material, by choosing the objects recognized as the smallest unit of a particle, judging from their apparent geometric form, from an image of a cross-section of the catalyst layer containing the hydrophilic material obtained with an EDX linked with the electron microscope, by measuring the largest traverse lengths of at least 50 particles of the hydrophilic material randomly selected and calculating the average length. the catalyst-on-support comprising a support which comprises an electroconductive inorganic oxide and a catalyst supported on the electroconductive inorganic oxide, the hydrophilic material being an agglomerate comprising hydrophilic electroconductive particles, the hydrophilic electroconductive particle having a particle size d1 of 10 to 100 nm, the hydrophilic material being present in an amount of 2 mass% or higher and lower than 20 mass% relative to the sum of the support and the hydrophilic material, the ratio of the particle size d1 to the particle size D being 0.5 to 3.0, the ratio of the particle size d2 to the thickness T being 0.1 to 1.2, wherein the catalyst comprises platinum; an alloy of platinum and a noble metal other than platinum; or an alloy of platinum and a base metal, wherein the hydrophilic electroconductive particles of the hydrophilic material and the support comprise at least one of an indium-based oxide, a tin-based oxide, a titanium-based oxide, a zirconium-based oxide, a selenium-based oxide, a tungsten-based oxide, a zinc-based oxide, a vanadium-based oxide, a tantalum-based oxide, a niobium-based oxide, and a rhenium-based oxide, wherein the particle sizes of the hydrophilic particle and the catalyst-on-support are determined by observing at a 100,000 times magnification in an electron micrograph a cross-section of a catalyst layer, by choosing the objects recognized as the smallest unit of a particle, judging from their apparent geometric form, by measuring the largest traverse length of 500 or more particles and calculating the average length, and wherein the particle size of the hydrophilic material is determined by observing at a 10,000 times magnification in an electron microscope a cross-section of a catalyst layer containing the hydrophilic material, by choosing the objects recognized as the smallest unit of a particle, judging from their apparent geometric form, from an image of a cross-section of the catalyst layer containing the hydrophilic material obtained with an EDX linked with the electron microscope, by measuring the largest traverse lengths of at least 50 particles of the hydrophilic material randomly selected and calculating the average length.