The purpose of this research was to study organizational health levels of elementary schools as classified by school size in the early stage of education reform. Data for this study were collected from all 99 elementary schools in Nonthaburi Province. All teachers in each school served as informants. The employed research instrument was the Elementary School Organizational Health Inventory based on Hoy and Feldman’s concept. It was used to assess three hierachical levels and eight health dimensions, namely, the institutional level (with dimensions of goal setting, and institutional integrity), the managerial level (with dimensions of collegial leadership, instructional leadership, and communication), and the technical level (with dimensions of academic emphasis, teacher morale, and instructional activities). The organizational health was classified into three levels: fully healthy, moderately healthy, and unhealthy. The employed statistics for data analysis were the percentage, percentile, mean, standard deviation, and standard score. Research findings were as follows: (1) The overall and every dimension of organizational health of the total number of 99 schools comprising small, medium sized, and large schools were at the moderately healthy level. (2) When the organizational health of each school was analyzed, the percentages of schools with fully healthy, moderately healthy, and unhealthy levels were as follows: 37, 39, and 25 for small schools; 12, 58, and 30 for medium sized schools; and 18, 64, and 18 for large schools, respectively. (3) When each school’s organizational health was analyzed by dimensions, it was found that more than 33 percent of small schools were unhealthy on the dimension of academic emphasis (technical level); above 30 percent of medium sized schools were unhealthy on the dimensions of goal setting, institutional integrity (institutional level), instructional leadership (managerial level) and teacher morale (technical level); forty percent of large schools were unhealthy on the dimension of collegial leadership (managerial level). After this preliminary study, effects of each organizational health level and its dimensions on the educational quality will be analyzed and strategies on personnel development for each level will be developed to suit Nonthaburi situation.