In achieving a digital transformation, one of the largest state-owned banks in Indonesia is trying to develop systems and applications that support its business processes. Based on the Project Status Report 2020, the success rate of the project was only 66%. In assessing the maturity level of APD group project management, the researcher would use the Project Management Maturity Model (PMMM) by Kerzner that applied PMBOK as a guideline. However, the existing questionnaire had not covered ten knowledge areas of PMBOK and used the old version of PMBOK that used Human Resource Management over terms of Resource Management. Thus, the researcher validated the PMMM Kerzner questionnaire before used it to assess the project management maturity level. This study aims to validate the questionnaire of PMMM Kerzner, confirmed the importance of using all PMBOK's areas, and formulate a final questionnaire. The researcher used the qualitative method by interviewing five experts using confirmatory questions and designated twenty-four questions. The researcher analyzed the data and information gathered using thematic analysis. The analysis result conveyed that four out of five experts agreed that PMBOK's ten knowledge areas should be measured. Moreover, the experts gave feedback and improvement input to the twenty-fourth question. This study output was a validated and completed PMMM questionnaire that relevant be used to measure the maturity level of project management. © 2021 IEEE.