Objective To perform the linguistic and psychometric validation of the Brazilian Portuguese version of the questionnaire Newcastle Asthma Knowledge Questionnaire on knowledge of asthma. Methods Two translations into Brazilian Portuguese of the Newcastle Asthma Knowledge Questionnaire were compared, creating a preliminary version. Seventeen questionnaires were administered to academics and health professionals for possible adjustments of the linguistic translation. Next, internal validation, and analysis of reproducibility and agreement were conducted using Cronbach’s coefficient, test and retest, and Kappa analysis. Results Only question number two required linguistic/cultural adaptation. The mean score of the knowledge on asthma of 78 participants was 20.81±3.81 points. The group of physicians got a mean score of 22.94±2.40 points, and other health professionals got a mean score of 19.07±3.88 points. Regarding the internal consistency analysis for the total score, the instrument obtained Cronbach  values of 64.4 for the minimum score, and 70.7 for the maximum score. Conclusion The Brazilian Portuguese version of the questionnaire Newcastle Asthma Knowledge Questionnaire was effective linguistically and psychometrically, presenting good internal consistency and reproducibility.