PURPOSE: To obtain a polyolefin for which no removal of catalyst residues is necessary because of a high activity of the catalyst, by contacting an olefin with a catalyst comprising a specified solid catalyst component and an organometallic compound.

CONSTITUTION: A solid catalyst component is obtained by reacting a solid obtained by reacting 1mol of C-Mg bonds in a solid obtained by reacting an organomagnesium component of the formula with at least one Ti or V compound in the presence (absence) of an inorganic solid selected from among inorganic (hydr)oxides, inorganic silicates, carbonates, sulfates and double salts, solid solutions and mixtures thereof with 0.05W20mol of a compound selected from among aldehydes, silanes, hydrogensiloxanes and (thio)alcohols with a component selected from among organoaluminum compounds, organomagnesium components and halides of Al, Sn or Si. An olefin is polymerized in the presence of a catalyst comprising 1g of the above solid catalyst component and 1W3,000mmol of an organometallic compound.