The present invention relates to a process for preparing silodosin with high optical purity up to 99.9% enantiomeric excess (e.e.) or above. The process makes use of a method step, in which the enantiomers contained in a racemic mixture of a compound represented by the general formula V: wherein * denotes the asymmetric center, R1 is a protecting group, and R2 is cyano or carbamoyl, are separated.