Résumé : The kinetic study of the solvolysis of m-CH 3, p-CH 3, m-OCH 3, p-Cl, m-Cl and p-F substituted α-phenylethyl chlorides has been carried out in the following media: water 20·5%-dioxane 79·5% water 49·3%-dioxane 50·7% water 66·66%-dioxane 33·33% water 5·3%-dioxane 25·8%-formic acid 69·7% water 6·1%-dioxane 39·8%-formic acid 54·1% water 5·8%-dioxane 60·2%-formic acid 34·0% Correlation of solvolysis rates has been made with the equations of Hammett, Winstein-Grünwald and Tommila. © 1961.