An organic phosphorous compound represented by the following formula (I): ##STR1## wherein R.sup.1, R.sup.2, R.sup.5 and R.sup.6 represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkylcycloalkyl group, an aralkyl group or a phenyl group; R.sup.3 represents a hydrogen atom or an alkyl group; R.sup.4 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkylcycloalkyl group, an aralkyl group or a phenyl group, or the two R.sup.4 may be combined with each other to form a direct bond, a sulfur bond (--S--), or aN optionally substituted methylene group; R.sup.7 and R.sup.8 represent a hydrogen atom or an alkyl group, or R.sup.7 and R.sup.8 may be combined with each other to form an alkylene group; A represents an alkylene group; B represents a direct bond or an alkylene group; and one of Y and Z represents a hydroxyl group, an alkoxy group or an aralkyloxy group, and the other one represents a hydrogen atom or an alkyl group; and the organic phosphorous compound is useful as a stabilizer for an organic material.