A process for the preparation of bis-acylphosphanes of formula R1P(COR )2 wherein R1 is unsubstituted phenyl or phenyl substituted by one to five halogen, C1-C8-alkyl, C1-C8-alkylthio and/or C1-C8-alkoxy; R2 is C1-C18-alkyl or C2-C18-alkenyl; C1-C18-alkyl or C2-C18-alkenyl substituted once or more than once by halogen —OR10, —OCO—R10, —OCO-Hal, —COO—R10, —N(R11)—CO—R10, —N(R11)—CO-Hal, —CO—NR11R10, —CH═CH—CO—OR10 or —CH═CH-phenyl; —C(C1-C4alkyl)=C(C1-C4alkyl)-CO—OR10 or —C(C1-C4alkyl)=(C1-C4alkyl)-phenyl; C5-C12cycloalkyl, C2-C18alkenyl, phenyl-C1-C4alkenyl, phenyl, naphthyl, biphenyl or a 5- or 6-membered -0-, S— or N-containing heterocyclic ring, the radicals phenyl, naphthyl, biphenyl or the 5- or 6-membered -0-, S— or N-containing heterocyclic ring being unsubstituted or substituted by one to five halogen, C1-C8alkyl, C1-C8alkoxy and/or C1-C8alkylthio; the process comprises the steps in a) selective reduction of dichlorophenylphosphanes of the formula R1P(Cl)2 by means of hydrogen at a temperature in the range from 20 to 200° C. and under hydrogen pressure of atmospheric pressure to 20 bar in the presence of a hydrogenation catalyst, a tert. aliphatic amine or an aromatic amine and in the presence of a non protic solvent which is unreactive under the hydrogenation conditions to obtain cyclic phenylphosphanes (R1P)n (n=4 to 6); or b) selective reduction of R1P(Cl)2 by means of hydrogen at a temperature in the range from 80 to 250° C. and under hydrogen pressure of 25 to 250 bar in the presence of a hydrogenation catalyst, a tert. aliphatic amine or an aromatic amine and in the presence of a non protic solvent which is unreactive under the hydrogenation conditions to obtain R1PH2; c) subsequent reaction with an acid halide of formula in the presence of an apropriate base R2COHal wherein R2 is as defined above.