This research aims to study, compare and develop guidelines of the internal quality assurance of basic education institutions in Chachoengsao Educational Service Area Office 2. The samples used in this research were 513 people comprising of education administrators, educators responsible for the internal quality assurance and teachers. Five-rating-scaled questionnaires were used for research instruments.  Statistics used to analyze the data obtained were frequency, percentage, mean, standard deviation, t-test and one-way ANOVA. The findings were that; 1) the implementation of the internal quality assurance of institutions in Chachoengsao Educational Service Area Office 2 both in overall and in each factor was at a high level: the factor of implementation, preparation and report, respectively, 2) the result of comparison regarding to implementation of the internal quality assurance of institutions in Chachoengsao Educational Service Area Office 2, classified by duty and position, was significantly different at .05 level.  In terms of each factor, it was found that, the factor of planning, assessment and evaluation and self-assessment report were significantly different at .05 level.  When compared regarding to the size of institution and working experience, the result was significantly different at .05.  When classified by the education level both in overall and in each factor, it showed that the opinions of teachers with different levels of education were the same except the opinions on appointment of responsible committee that were significantly different at .05, 3) implementation guidelines of the internal quality assurance of basic education institutions in Chachoengsao Educational Service Area Office 2 included the following items. (1) The internal quality assurance of institutions should be implemented by both levels of administration and operation. (2) Persons in charge for implementation such as administrators, Deputy of Academic Director should be Vice-Chairman, Head of Department should be committee, Head of Assessment and Evaluation should be committee and secretary etc.  (3) Planning, implementation as well as assessment and evaluation should be done clearly and continuously. The internal quality assurance of institutions should be implemented practically and authentically.  The process should be assessed and continual improvement should be done.  The course should be arranged to be consistent with the learners life. (4) Technology, computers and other materials should be facilitated.