The Competency-Based Education system, introduced in 2007, intended to model the education system in Sri Lanka to prepare a workforce with adequate skills and knowledge for the dynamic world of work. This paper investigated the challenges faced by teachers in applying the Competency-Based mathematics teaching process in Sri Lanka from three perspectives: low understanding of CBE concepts and insufficient in-service training, need for more support facilities and teaching-learning resources, and low student cooperation during the teaching process. The study employed a quantitative approach. Data was collected from 276 middle school mathematics teachers from the Western Province of Sri Lanka. The primary data collection instrument was a questionnaire. The data was statistically analysed using descriptive statistics such as frequency, percentages, mean, and mode. The results confirmed that teachers faced challenges that impeded the successful application of CBE in the teaching process. The results suggested that every teacher in the country to undergo a strong awareness programme. Thereby, establishing a mechanism for teachers to engage in a professionally realistic period in keeping with international standards. Further, allocate a period for professional development activities, which will reward them periodically, and the teachers’ involvement in the curriculum development process. The Ministry of Education, with the help of other stakeholders, to devise ways of providing quality and relevant teaching resources, including IT facilities that are consistent with the CBE curriculum.