Provided is an electrocatalyst for solid polymer fuel cells capable of increasing the active surface area for reactions in a catalyst component, increasing the utilization efficiency of the catalyst, and reducing the amount of expensive precious metal catalyst used. Also provided are a membrane electrode assembly that uses this electrocatalyst and a solid polymer fuel cell. An electrocatalyst (1) for a solid polymer fuel cell is provided with a catalyst (2) and solid proton conducting material (3). A liquid conductive material retention part (4a) that retains a liquid proton conducting material that connects the catalyst (2) and solid proton conducting material (3) is provided between the same. The surface area of the catalyst (2) exposed within the liquid conductive material retention part (4a) is larger than the surface area of the catalyst (2) in contact with the solid proton conducting material (3).