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Solvolysis rates of 2-(dimethylphenylsilyl)-1-(Y-phenyl)ethyl 3,5-dinitrobenzoates were determined conductimetrically in 60% (v/v) aqueous ethanol. In order to clarify the nature of the β-Si participation quantitatively, the effects of α-aryl substituents on the rates were analyzed by means of the Yukawa–Tsuno Eq. The α-aryl (Y)-substituent effect at 25 °C was correlated with r 1.0 and ρ = −3.0, which is significantly reduced compared with that of −5.45 for the non-silylated 1-arylethyl system. There is a linear relationship between logkY/kH of silylated and non-silylated substrates: log(kY/kH)Si = 0.52log(kY/kH)non-Si. This is the same form as the extended Brønsted relationship. The Brønsted coefficient α = 0.52 appeared to be consistent with the neighboring silyl-participation in the silyl-bridged transition state.