The purpose of the paper was to investigate how collaboration and mutual support as the processes established by communities of practice to improve continuing professional teachers' development in high schools. This study is essential as it helped teachers to see the importance of working as teams through mutual support given to each other to boost their professional development. The study was qualitative in nature; semi-structured interviews were conducted in order to get expedient and in-depth information from the participants with the use of case study design. The study found that teachers participated effectively and had mutual relationship in collaborative learning activities in communities of practice. The findings indicated that teachers should collaborate and mutually engage in learning activities in communities of practice in high schools in order to enhance their professional development.