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. Further, we explore necessary tools for such an approach, like Semantic Web annotation tools and specific domain authoring tools, as well as domain XML formats and transformation techniques. Additionally, we give a conceptual overview of a course authoring tool that fully support the proposed approach.