PurposeThis paper aims to discover the effectiveness of Farsi-English query using ontology.Design/methodology/approachThe present study is quasi-experimental. The sample consisted of 60 students and graduate and doctoral staff from Shiraz University and the Regional Center for Science and Technology. A researcher-made questionnaire was used to assess the level of English language proficiency of users, background knowledge and their level of satisfaction with search results before and after using ontology. Each user also evaluated the relevance of the top ten results on the Google search engine results page before and after using ontology.FindingsThe findings showed that the level of complexity of the task, the use of ontology, the interactive effect of the level of complexity of the task with the domain knowledge of the users, and the interactive effect of the level of complexity of the task with ontology, influence the effectiveness of retrieval results from the users' point of view. The results of the present study also showed that the level of complexity of the task, the use of ontology, and the interactive effect of the level of complexity of the task and the use of ontology, affect the level of user satisfaction.Originality/valueThe results of this research are significant in both theoretical and practical aspects. Theoretically, given the lack of research in which the interactive effect of the use of ontology has examined the level of complexity of tasks and domain knowledge of users, the present study can be considered as an attempt to improve information retrieval systems. From a practical point of view, the results of this research will help researchers and designers of information retrieval systems to understand that the use of ontologies can be used to retrieve information and improve the query and assess the needs of users and their satisfaction in this field, and ultimately, making the information retrieval process more effective.