Catalytic properties of the binary phosphorus-molybdenum system with Mo/P = 3 -24.5 in acrolein oxidation have been studied. The selectivity to acrylic acid and carbon oxides practically does not depend on the chemical composition of the system, and the maximum activity is observed for Mo/P = 12. The catalytic properties of the system are determined by an X-ray amorphous phase, apparently molybdenyl phosphate.