Abstract: Sterically hindered 4-substituted-2,6-di-t-butylphenyl bis (substituted phenyl)phosphites form effective and improved antioxidant combinations with hydroxyphenylalkyleneyl isocyanurates. These systems provide enhanced antioxidant activity activity in organic materials subject to degradation by heat and oxygen, and are especeially effective in polymers such as the poly(olefins) represented by poly(propylene). The triphenyl phosphites are readily prepared by reacting a 2,6-di-t-butyl-4-substituted-phenylphosphorodichloridite with a sodium salt of a 2-t-butyl-substituted phenol.