The objectives of this study were 1) to examine the states of teachers’ competency, 2) to compare teachers’ competency according to work experience; and 3) to investigate guidelines for developing teachers’ competency in small-sized schools under Primary Educational Service Area Office 2. The samples were 327 school administrators and teachers which were determined by using Krejcie and Morgan’s table and then simple random sampling by using lottery method was implemented. The research instruments were questionnaire with the reliability level of 0.970 and semi-structure interview which was implemented with 9 experts chosen by purposive sampling. The collected data from the questionnaire were analyzed by using percentage, mean, standard deviation and Independent sample  t-test and the data gained from the semi-structure interview were analyzed by content analysis. The results suggested that 1) states of teachers’ competency in small-sized schools under Primary Educational Service Area Office 2 were at a high level in overall aspect, 2) comparison of teachers’ competency according to work experience was not different in each and overall aspect and 3) guidelines for developing teachers’ competency in small-sized schools were that school administrators should encourage teachers in terms of learning management, learners’ development, administration and conducting action research for learners’ development.