The purpose of this study is to determine the teachers' self-efficacy in terms of their former experience and professional development in the Turkish World (Turkey and Kazakhstan) based on TALIS 2018 Data. In this context, this study is conducted with the participation of 6.531 Kazakh and 3.828 Turkish teachers who teach at ISCED level 2. The data for this study are obtained from the official internet website of OECD. The results are obtained by utilizing three separate regression analyses by using IDB Analyzer program based on SPSS. According to the results, it is determined that the variance of teachers' former experience explains 2% of the variance in their self-efficacy in Turkey; 3% in Kazakhstan. On the other hand, the variance of teachers' former experience explains 3% of the variance in their professional development in Turkey; 4% in Kazakhstan. However, the variance of teachers' professional development explains 32% of the variance in their self-efficacy in Turkey; 23% in Kazakhstan. Moreover, there is a positive and significant relationship between both the self-efficacy and professional development of teachers (e.g. 'teaching practice', 'professional cooperation in lessons' and 'effective professional development') in Turkey and Kazakhstan. Therefore, it is important to support teachers' continuous professional development and empowerment to increase their self-efficacy through continuous professional development programs which focus on the practice, especially classroom practices. In addition, to prepare the qualified continuous professional development programs, faculties of education might strengthen their capacity to provide in-service training as well as pre-service training.