The invention relates to an process for preparing Tamsulosin hydrochloride of Formula (I) which comprises (i) reacting (R)-(−)-5-(2-amino-propyl)-2-methoxybenzenesulfonamide of Formula (II) with substituted phenoxy compound of Formula (III), wherein Z represents a removing group, such as —OSO2CH3, —OSO2C6H4CH3, —F, —Br, —Cl, or —I, in a solvent in the presence of an alkaline earth metal oxide to obtain Tamsulosin base and (ii) converting Tamsulosin base into hydrochloride salt in a solvent by addition of aqueous hydrochloric acid.