A process for preparing optically pure enantiomers of R-(-)tamsulosin of formiula Ia and S-(+)tamsulosin of formula Ib by resolving racemic tamsulosin of formula I by means of (IR)-(-)-camphor-10-sulfonic acid and (1S)-(+)-camphor-10-sulfonic acid, resp., in an environment of organic solvents, water or mixtures thereof. ##STR1##