The aim of this study was to construct professional development indicators for the principals of elementary and junior high schools and then test in the validity and reliability through a questionnaire. The process consisted of three stages. At first, the researcher reviewed a wide range of literature related to professional development to compile a list of ten patterns associated with the professional development of principals. Second, eight experts were assembled for a focus group to examine the indicators. Nine other experts evaluated the questionnaire for content validity before drafting a preliminary version of the questionnaire. Finally, the revised version was trial-tested and revised as the final version to test the indicators. The proposed questionnaire was found to have acceptable reliability and validity. A number of practical recommendations were made for administrators and principals of elementary and junior high schools.