Abstract: Knowledge has been regarded as a pivotal part of interpreting competence, yet there is still a dearth of study, especially on “relevant knowledge”, i.e., the ad hoc knowledge pertaining to a specific interpreting task.In this study, semi-structured interviews were conducted with 8 professional interpreters after they finished two interpreting tasks, with an aim to unveil the content, purpose, scope and degree of specialization of the relevant knowledge in interpreting mode.The results show that interpreters need to know about domain-specific expressions and concepts via the source and/or the target language, while the ultimate purpose is to acquire professional and logical delivery in the target language.Relevant knowledge is not limited to one specific domain, and its degree of specialization may vary, but the scope is determined by conference details such as PPT, manuscript, and agenda.Therefore, the relevant knowledge in interpreting mode is not equal to domain knowledge, and is mainly composed of the logical delivery of the knowledge about relevant domain(s), as well as relevant information as a source to anticipate the content and scope of the knowledge needed.