A catalyst for olefin polymerization comprising (A) a solid catalyst component prepared by causing (a) a magnesium compound, (b) a tetravalent titanium halide compound, and (c) an electron donor compound to come in contact with each other, (B) an organoaluminum compound of the general formula R.sup.1.sub.pAlQ.sub.3-p, and (C) an oligomer of an organosilicon compound of the following chemical formula; R.sup.4--(R.sup.2R.sup.3SiO).sub.m--R.sup.5 can produce olefin polymers having higher stereoregularity and a broader molecular weight distribution in a higher yield than conventional catalysts.