This paper proposes to analyze the problematic of materiality in Althusser's theory of ideology, which has long been neglected by most of his commentators. Althusser's particularities and limits are discussed as well. ”Ideological state apparatuses” (ISA) as proposed by Althusser uncovers the hidden class struggle in the existing relations of production and the role assumed by different kinds of ISA. In addition, ISA as a concept reexamines the essence of ideology and exposes Althusser's imaginary and material characteristics. And yet, materiality in his sense can be built only in the foreclosure of the materiality of ideology itself and is only the effects of ideology. It is not until his last days that, through rethinking materialism and recognizing different modalities of the material, Althusser finally touches upon the possibilities of ideology itself.