Teacher training is one of the most important aspects of professional development for teachers in education. This paper identified 22 primary in-service teachers' beliefs, needs, and challenges they faced with regards to teacher training program in Thailand. The research methods used were a modified questionnaire and individual and focus group interviews. Findings revealed that the beliefs of the primary teachers were shaped by their previous attendance and experience on teacher's training programs in the country. Engaging workshops, simple but relevant teaching strategies were reported to be the needs of these teachers in a teacher training program. Teachers also reported the lack of teaching resources, problems on implementing new teaching strategies, and a big class size as the challenges they have encountered in their own classrooms. Findings may be useful for the Ministry of Education, education policy-makers, and teacher's training institutions in the ASEAN region context to design a much more effective training program for the local teachers to improve their teaching capacity. Implications are discussed in the study.