The questionnaire development process consisted of the following steps: content and face validation, and reliability analysis. The questionnaire contains items assessing parents' literacy of body posture and was conducted on 55 Polish parents of school-age children and adolescents. Initial results (first test-retest) of 37 participants revealed substantial reliability (0.61 to 1.00) however, it was revealed that modifications were needed for some specific questions. After revisions and retesting (second test-retest of 18 participants), the updated questionnaire demonstrated significantly improved reliability (Cohen's kappa coefficient ranged from 0.85 to 1.00). The developed questionnaire is valid -in terms of face validity, content validity, and reliability for assessing parents' literacy of body posture, and can potentially be used in clinical trials and practical settings.