To 1) study the operation of bilingual schools, 2) study supportive and obstacle factors in operating of bilingual school, 3) compare the operation of supportive factors and the obstacle factors' of bilingual schools in Bangkok metropolitan and up country area. Employing qualitative research as a multicase study research for two schools consisted of Benjamarachutit and Wat Nairong School. The research data were collected by analyzing related documents, employing participatory and non- participatory observations as well as interview and focus group technique. The research data were analyzed by employing content analysis, inductive conclusion and comparison. The research results were as follows 1) The operation planning were found that both of two cases study had a systematic operation planning. Benjamarachutit School used 10 months for planning the opening of the program, while it took Wat Nairong School 4 months under the surveillance of the assistant school. 2) The structure organizing were found that Benjamarachutit School organized the structure into 4 sections. Mean while the English program had its own organized structure. Wat Nairong School didn't separate its structure form the regular program (the main school) because students in the program were the majority of the school. 3) Executing were found that Benjamarachutit School offered the English program in four group of subjects which were taught by Thai and English teachers who worked for annual contract. There were only payment rate that depended on races, the welfares were provided, the buildings and media were available, the allocation of fiscal was impartially. Strong relationship existed between schools and communities. English is compulsory used in class. However, Wat Nairong school offered English program in six group of subjects. There were foreigner boarding teachers and Thai special teachers who worked for annual contract. Payment rate depended on races and no welfares provided. Buildings and classrooms were quite convenient and ready unlikemedias. School budgets were systematic organized. The relationship between school and community was poor when international program was firstly started but it had been developing in positive ways later. The main language used in class is English but with Thai translation sometime. 4) Evaluating result of two cases study were found that there were project evaluation from students and guardians every years. 5) The similar supportive factors in both of two schools consisted of appropriate class size, systematic fiscal management, students' family background and participation of guardians. The different supportive factors of Benjamarachutit School consisted of school reputation, medias and instruments availability, furthering study result, development of teacher quality, student quality and Wat Nairong School consisted of systematic school management, project's public relations and the proficiency of special teachers. 6) The similar obstacle factors in both of two schools consisted of giving up teachers' contract, the teachers who were not graduated in education, non readiness on language of students and the guardians' expectation. The different obstacle factors of Benjamarachutit School were the time for period changing and the difficulty in finding teachers and Wat Nairong School consisted of the special teachers' time for students was less.