Abstract: A process for the preparation of phosphonium salts by the use of chlorides, which is useful in the course of synthesis of olefin compounds by the Wittig reaction, and which comprises reacting a phosphine compound of the general formulaR.sup.1.sub.3 Pwherein R.sup.1 is a phenyl group or a straight-chain alkyl group having 2 to 8 carbon atoms, with a primary or secondary chloride of the general formula ##STR1## wherein R.sup.2 and R.sup.3 are hydrocarbon radicals, in a solvent selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide and N,N-1,3-dimethyl-2-imidazolidinone, and in the presence of an alkali metal salt of the general formula MBr or MI.