The purposes of this research were 1) to study the characteristics of school administrators in Thai primary schools, 2) to develop the characteristics of the Brahmaviharadharma Principles for Thai school administrators, and 3) to propose a model of developing the characteristics of the Brahmaviharadharma Principles for Thai school administrators. Mixed methods research was designed, and the instrument used in the research was a questionnaire distributed to 390 administrators in primary schools, interview form by interviewing 24 key informants, and questions for focus group discussion with 17 experts. Qualitative data from in-depth interview and focus group discussion were analyzed by using content analysis whereas quantitative data were analyzed by using percentage, frequency, mean, standard deviation. Results showed that 1) the characteristics of the school administrators in Thai primary schools consisted of 4 aspects which were 1) knowledgeable and capable, 2) social maturity and generous, 3) accountability, and 4) good human relations in the overall level was very high. Considering to each aspect was also at a high level in all aspects. 2) The characteristics of the Brahmaviharadharma Principles for Thai school administrators was the operation in all 4 aspects of the school, which were (1) academic administration, (2) budget administration, (3) human resource management, and (4) general administration. The principle of Brahmaviharadham is a principle that must be kept in mind and supervised behavior that suitable for executives with 4 areas which are (1) compassion, (2) kindness, (3) happy when others are happy, and (4) neutral mind. 3) A model of developing the characteristics of the Brahmaviharadharma Principles for Thai school administrators was called C B S Model which consisted of 3 important points which were 1) Characteristics (C), characteristics of school administrators was the physical characteristics and expression of the behavior of the person who is a part of character which was shown to others for Thai primary school administrators in 4 aspects which composed of (1) have knowledge and ability, (2) have social maturity and generous, (3) accountability, and (4) good human relations. 2) Brahmaviharadhamma (B), it is a principle that must be kept in mind and supervised behavior and suitable for executives with 4 areas which consisted of (1) compassion, (2) kindness, (3) happy when others are happy, and (4) neutral mind. 3) School (S), School administration was the operation in all 4 aspects of the school, which were (1) academic administration, (2) budget administration, (3) human resource management, and (4) general administration.