This study examined teachers' concerns about including students with disabilities (SWDs) in regular classrooms and identified the background variables that were significantly associated with their concerns. A total of 1008 primary school teachers from 236 schools across all 25 provinces and cities in Cambodia participated in the study. The Concern about Inclusive Education Scale (CIES) was used as a research instrument. Descriptive statistics, a principal component analysis, reliability tests, Pearson correlation coefficients and a multiple regression analysis were used for data analysis. The result of the principal component analysis confirmed a four-factor model for the CIES. The study found that Cambodian teachers had high levels of concern about including SWDs in regular classrooms. They expressed the deepest concerns about the inadequate availability of special education instructional materials and teaching aids, the lack of knowledge and skills required to teach SWDs, the increased workloads and the challenges of providing equal attention to all students. The experience of inclusive education training, years of teaching in regular classrooms, and experience of teaching SWDs were significantly associated with their concerns about inclusion. The findings were discussed with practical implications for improved policy and practice to address Cambodian teachers' concerns and promote their inclusive practices.