Relative rates of chlorine atom abstraction by organosilyl radicals were determined by allowing six different polychloroalkanes to compete in pairs for an insufficient amount of triethylsilane, phenyldimethylsilane, diphenylmethylsilane and ethyldichlorosilane at 80°C in the presence of benzoyl peroxide. Relative reactivities per chlorine atom of the trichloromethyl groups in X-CCl₃ towards the four organosilyl radicals are satisfactorily correlated with the Taft σ values of the substituents X. These relationships can be interpreted in terms of the polar factor which is important in determining the reactivities of the chlorine atoms in this class of substrates. In the absence of solvent, the Hammett ρ values for the reactions of triethylsilyl, phenyldimethylsilyl, diphenylmethylsilyl and ethyldichlorosilyl radicals are 0.29, 0.27, 0.29 and 0.29, respectively. It was also found that the selectivity of the reaciton in methyl ethyl ketone or methyl acetate was somewhat greater than that in cyclohexane, benzene and chlorobenzene.