Objective: to develop and validate an instrument to assess the knowledge of oncology nurses about the fully implanted central venous catheter. Methods: this is a methodological study. The instrument was built based on an integrative review and included 25 questions (10 about general aspects of the device and puncture; 10 about heparinization and complications; and 5 about the dressing). After construction, the instrument was evaluated by five experts, in a single round, in four items, on the adequacy of the questions to the objectives of the instrument, the valuation of the questions, the content and the clarity of each question. Adequacy was confirmed by the minimum Concordance Index of 80%. Results: all items in the questions about heparinization and complications were considered adequate, and two questions about general aspects and puncture and one question about dressing had an agreement rate of 60%. Changes were made as suggested by experts. Conclusion: the instrument, for the most part, presented clear, relevant questions that serve the purpose. Contributions to practice: it is expected to contribute with institutions and with a safe care of nurses who assist cancer patients with fully implanted catheters.