A solid catalyst component for olefin polymerization catalysts prepared by subjecting diethoxymagnesium (a), calcium chloride (b) and a silicon compound (c) of the general formula: Si(OR).sub.4 (wherein R is an alkyl or aryl group) together to a contact treatment in the presence of an organic solvent (d), suspending the treated composition in an aromatic hydrocarbon (e) which is liquid at normal temperature and bringing the suspension into a first contact with titanium tetrachloride (f) to form a product and bringing it to a second contact with titanium tetrachloride (f) in such manner that a diester (g) of an aromatic dicarboxylic acid is allowed to coexist at any stage of the above suspending and/or contacts with the exception of the contact treatment, the calcium chloride (b) being used in an amount of 1-2 g per gram of the diethoxymagnesium (a). This solid catalyst component exhibits, when applied to the polymerization of olefins, a surprisingly enhanced polymerization activity per titanium atom and a high stereospecific performance and scarcely necessitates any deashing treatment, thus affording a great economical advantage.