The objectives of this research were: 1) to study the elements and indicators of primary school teachers' critical thinking, 2) to study current situation, desirable situation, development technique, and need for developing the primary school teachers' critical thinking, 3) to develop the program for developing the primary school teachers' critical thinking, and 4) to study the findings of usage in development program for primary school teachers' critical thinking by using Research and Development. The samples were 384 primary school teachers, and 34 volunteered teachers to participate in development by using questionnaire, evaluation form, and tests. The statistic using for data analysis included the percentage, mean, standard deviation, modified priority needs index (PNI[subscript modified]), and t-test. The research findings found that: 1) the elements and indicators of primary school teachers' critical thinking consisted of 3 elements and 12 indicators of critical thinking ability, and 6 elements and 24 indicators of critical thinking disposition, 2) the current situation of primary school teachers' critical thinking was in "High" level, for desirable situation, it was in "The Highest" level, 3) the development program, consisted of: the principles, objectives, contents, and development activities included 4 Parts, Part 1: the readiness preparation, Part 2: training, Part 3: integration with work practice, and Part 4: posttest, and measurement and evaluation. 4) The posttest score was significantly higher than the pretest score at 0.01 level.