Objective: To validate an instrument for assessment of knowledge of nursing students about the blood pressure measurement. Method: methodological study conducted with 27 judges nurses, teachers of the discipline of semiology and / or semiotics, with at least 1 year of experience in the disciplines, in three stages: literature review for the development of the knowledge questionnaire, submission to the judges; and content validation by the Kappa index, accepting the value > 0,61, and content Validity Index (CVI ) > 0,75. Results: The 12 questions obtained Kappa and CVI within the parameters established for content validity, 7 showed perfect concordance index and 5 required modifications. Conclusion: It was not necessary remove questions of the instrument, which expresses that they have representation and extension about the domain of interest, facilitating the assessment of knowledge