The purposes of this research were to study levels of performance in the internal supervision process, and to compare opinions of school administrators and teachers towards the performance in the internal supervision process of the primary school administrators under the Office of Angthong Provincial Primary Education in four aspects : assessment of current situation, problems and needs, supervision planning, supervision performance, and supervision evaluation, as classified by position and experience in school administration. The sample used in this research were 131 school administrators, and 316 teachers, totalling 447. The instrument used for collecting data was the rating scale questionaire. The statistics used for analyzing data were mean, standard deviation, and t-test. The main research findings were summarized as follows :- 1. The school administrators and teachers percived the level of performance in the internal supervision process of the school administrator at the moderate level. However, when considered by aspects it was found that in almost all aspects was at a moderate level, except in the aspect of supervision performance at a high level. 2. The school administrators and teachers differently perceived the level of performance in the internal supervision process of the school administrators in overall and individual aspects with statistical significance at the .01 level. 3. The school administrators with different experiences in school administration differently perceived the level of performance in the internal supervision process of the school administrators in overall and supervision planning and supervision performance aspects with statistical significance at the .05 level, but in the aspects of assessment of current situation, problems and needs and supervision evaluation with no statistical significance. 4. The school administrators and teachers perceived the additional problems in the internal supervision process on limitation of personnel, administrators having too much work, and administrators having not enough knowledge on internal supervision process. 5. The school administrators and teachers suggested that there be meeting on internal supervision, examples and models of good internal supervision process, and teachers participating in overall internal supervision process.