This action research project sought to investigate the role of explicit citation vocabulary instruction in the learning of citation style guidelines for an English for Academic Purposes (EAP) writing course at an English-medium university in Northern Thailand. The participants consisted of 120 undergraduate students enrolled in the EAP writing class who were divided into an experimental group and a control group. The class included a step-by-step essay writing assignment that included source selection and use of quoted material from sources. Participants in the experimental group were exposed to a multi-week treatment in which citation vocabulary terms were reviewed in subsequent lessons. All participants were assessed through a citation quiz and the citation part-score on the rubric for the final draft of an essay. Results of the study were inconclusive about the effectiveness of a vocabulary approach on participants' ability to apply knowledge of citation style. Further research is needed on this topic.