Rate coefficients for the reaction of ground-state silicon atoms Si(P-3(J)) with acetylene and ethylene have been measured at temperatures down to 15 K. The experiments have been performed in a continuous flow CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) apparatus using pulsed laser photolysis of Si(CH3)(4) to generate Si(P-3(J)) atoms and laser-induced fluorescence to observe the kinetic decay of the atoms and hence determine the rate coefficients. Both reactions are found to be fast, and the reaction rates show a very mild dependence on temperature. The rate coefficients match the expressions k(Si+C2H2)=(2.6+/-0.6)10(-10) (T/300)-((0.71+/-0.24))exp(-(29 +/-10)/T)cm(3) molecule(-1) s(-1) and k(Si+C2H4)=(3.74+/-0.3)10(-10) (T/300)(-(0.34+/-0.10))exp(-(16 +/-4)/T) cm(3) molecule(-1) s(-1) in the temperature range 15-300 K. The nature of the products and the similarities of the carbon and silicon chemistry are discussed.