Abstract: A semipermeable membrane supporting material formed of a non-woven fabric comprising two or more main synthetic fibers having different fiber diameters and a binder synthetic fiber and having a semipermeable membrane application surface and a non-application surface having a semipermeable membrane application surface:non-application surface smoothness ratio of from 5.0:1.0 to 1.1:1.0, a semipermeable membrane supporting material formed of a non-woven fabric comprising a main synthetic fiber and a binder synthetic fiber, having an average breaking length of less than 4.0 km in the machine direction (MD) and the cross direction (CD) at an elongation by 5% and having a dimensional change ratio, measured under heat in the cross direction (CD), of ?0.3 to +1.0%, a spiral-type semipermeable membrane element including the above semipermeable membrane supporting material, and a process for producing a semipermeable membrane supporting material.