The paper proposes a framework for building learning object (LO) content using ontologies. In the previous work on using ontologies to describe LOs, researchers employed ontologies exclusively for describing LOs? metadata. Although such an approach is useful for searching for LOs in LO Repositories, it does not provide us with features to reuse components of LOs, nor to incorporate an explicit specification of domain semantics into LO content. We propose the use of two kinds of ontologies as a solution to this problem: content structure ontologies and domain ontologies.