The objectives of this research were: 1) to develop the training course of English instruction in Primary levels through Problem - Based Learning approach and 2) to investigate the effectiveness of the training course of English instruction in Primary levels through Problem-Based Learning approach implemented by teachers in SANUK province cluster. The research conduction was divided into two phases comprised of phase 1: step 1) study the related empirical documents research, principles and theories, and step 2) construct and develop the training curriculum, and step 3) implementation of the developed training curriculum. Phases 2 was the investigation and the improvement of the developed training curriculum. The research samples were 70 teachers who were selected through purposive sampling from teachers who participated in the Teacher Professional Development Project held by Sakon Nakhon Rajabhat University in 2016. The developed training course was investigated by five experts. The collected data were analyzed by software program for mean, percentage t-test for dependent samples and standard deviation in terms of quantitative data, and content analysis for qualitative data. The findings revealed that 1. The training curriculum on training course of English instruction in primary levels through problem-based learning approach comprised of 1) course objectives, 2) content structures, 3) training process and 4) training measurement and evaluation. 2. The efficacy of the developed training curriculum was presented as 1) the comprehension of English instruction in primary levels through problem-based learning approach after training was higher than before training with statistically significant at .01,2) the English instruction in primary levels through problem-based learning approach were at high level ( =4.45), and 3) the attitudes of teachers towards the developed training curriculum was at the highest level ( =4.86).