Today’s global society is full of advancement from the development of high-level technology. The study results shall be used as a guideline for developing educational institution administration to become stable and sustainable learning organizations in the future. This research aimed 1) to study levels of transformational leadership among administrators of private schools, 2) to study levels of effectiveness of educational institution administration among administrators of private schools 3) to study transformational leadership that affects effectiveness of educational institution administration of private schools and 4) to study a guideline to improve effectiveness of educational institution administration by using transformational leadership among administrators of private schools. The research was conducted on the basis of survey research design. The sample comprised 266 teachers. of private schools under Samut Sakhon Provincial Education Office. Key informants were 5 school administrators. The research results indicated as follows: 1) Overall and each aspect of transformational leadership among administrators of private schools under Samut Sakhon Provincial Education Office were at a high level, 2) Overall and each aspect of effectiveness of educational institution administration were at a high level, 3) Transformational leadership among administrators affected effectiveness of educational institution administration among administrators of private schools with the statistical significance level of 0.05, the multiple correlation coefficient was 87.80%, 4) Guidelines to improve effectiveness of educational institution administration by using transformational leadership can be summarized as follows: 4.1) Elements of transformational leadership that could be used to improve the effectiveness were intellectual stimulation and idealized influence, 4.2) Effectiveness of educational institution administration required strategic planning with PDCA, proactive policies, and advanced technology.