Ontologies provide shared and reusable pieces of knowledge about a specific domain. Building an ontology by hand is a very hard and prone to er-rors task. Ontology learning from existing resources provides a good solution to this issue. Databases are widely used to store data. They were often considered as the most reliable sources for knowledge extraction. NOSQL databases are more and more used to store data. MongoDB database is emerging as the fastest growing NOSQL database in the world. It belongs to the document oriented da-tabases variant. This paper proposes an approach to learn OWL ontology from data in MongoDB database and describes a tool implementing transformation rules.