A personalized service system and method based on an ontology is provided, in which if a user selects a personalized service while a subject or an object in a user profile ontology of user's personal information is associated with a subject or an object of a personalized service ontology through a relationship name, the system and method searches for a personalized service ontology corresponding to the selected personalized service, acquires personal information of an instance form in the user profile ontology associated with the personalized service ontology, executes the personalized service by applying the acquired personal information, and provides the user with a result of the execution.