Phosphorus-containing compounds of the formula: ##STR1## wherein R.sup.1 and R.sup.2 are each a hydrogen atom or a lower alkyl group, and R.sup.3 is a lower alkyl or phenyl group. These compounds may be used as stabilizers against the action of heat, light and oxygen for organic substances and especially polyolefin resins. These phosphorus-containing compounds may be used in conjunction with other stabilizers such phenol-type and sulfur-containing antioxidants, especially in polyolefin resin compositions to produce a polyolefin resin composition having excellent resistance to light, heat and oxygen. The present invention also relates to a method of producing the compounds of the aforementioned formula by reacting ##STR2## with a disubstituted phosphonate of the formula ##STR3## wherein R.sup.1, R.sup.2 and R.sup.3 are as defined above.