The kinetics of solvolysis of chlorodiethylphosphine, chloro(di-n-propyl)phosphine and chlorodiphenylphosphine was studied by conductometry in pure ethanol and in various mixed solvents, and was compared with that of dialkyl phosphorochloridites and of dialkyl and diaryl phosphinyl chlorides. The rate of ethanolysis of chloro(di-n-propyl)phosphine was found to be larger at higher initial concentrations. Addition of sulfuric or perchloric acid enhanced the rate of solvolysis, while sodium perchlorate and lithium chloride had no influence. In ethanof containing water, the rate of solvolysis of chloro(di-n-propylphosphine is approximately proportional to the concentration of water. In formic acid, the solvolysis of chloro(di-n-propyl)phosphine is slower than in ethanol. Addition of acetone to ethanol increases the rate of solvolysis of chloro(di-n-propyl)phosphine—possibly due to a condensation reaction producing a 1-chloroalkyl dialkylphosphine oxide. The rate of ethanolysis of chloro(di-n-propyl)phosphine is considerably enhanced in the presence of isobutylamine, di-n-butylamine and triethylamine. The solvolysis of di-t-butylphosphinyl chloride in absolute ethanol is very much slower than that of dimethyl and diethyl phosphinyl chloride.