The 21st Century has brought a lot of challenges in developing the professional leadership characteristics of school leaders. Their roles are no longer limited in implementing educational policies and objectives but have become responsible for raising the generations and qualifying them in a rapidly changing era. However, in Thailand, it was observed that there were Thai principals and school leaders who were not adequately trained for school leadership. This descriptive research surveyed the profile of the school administrators of secondary schools in Nakhon Nayok, Thailand as well as their level of practice of the 21st-Century professional leadership standards. A questionnaire checklist adapted from the frameworks of Kelly Lambert (2001) and The Wallace Foundation (2013) was used to gather data. Data analysis showed that the school administrators are females, with master's degrees, 55 years and older, and have few years of administrative experience. Further, they highly practiced the different 21st-century professional leadership standards; however, these were not influenced by their profile. Lastly, it was found out that there were no significant differences in the level of practice of the different 21st-century professional leadership standards as indicated by the profile indicators of the school administrators.