The purposes of this study were 1) to study the operation and problem of the internal quality assurance of the schools based on the internal quality assurance under Phetchabun Primary Educational Service Area Office 2 and 2) to compare the operation and problem of the internal quality assurance of the schools between respondents’ positions and size of schools. The samples of this study were 310 schools’ administrators and teachers using Krejcie and Morgan table and the stratified random sampling method. Statistics used for data analysis were percentage, mean, standard deviation, t-test and F-test. The study findings revealed as follows : 1. The operation of the internal quality assurance of the schools in total was at high level. 2. The problem of the internal quality assurance of the schools in total was at low level. 3. The comparison between the respondents’ position and the size of schools on the operation of the operation of the internal quality assurance of the schools in total was not different at a level of .05. 4.. The comparison between the respondents’ position and the size of schools on the problem of the operation of the internal quality assurance of the schools in total was not different at a level of .05.