A process for producing a saccharified solution in an improved yield when filtering the mixture obtained by saccharifying lignocellulosic biomass is provided. A mixture containing a saccharified solution and an undecomposed biomass residue by treating a substrate biomass using a saccharification enzyme is obtained. The mixture is filtered to obtain the saccharified solution as a filtrate. Before filtering the mixture, 95% by mass or more of the particles, based on the total amount of particles contained in a centrifuged supernatant of the mixture, is adjusted to have a particle size ranging from 1 to 30 μm.