GTD Ontology (GTDOnto) is an ontology proposed to define the concepts, vocabularies, and relations of terrorist incidents in the GTD using OWL format. This work is in progress and has been developed based on the NeOn methodology guidelines. The GTDOnto has been developed from scratch to define vocabulary and relations used for representing the incidents of the GTD dataset in a machine-readable format. The GTDOnto was implemented with the Web Ontology Language (OWL) using Protégé editor and two instances are included in the dataset as an example.