This study aimed to examine the underlying sources in developing chemistry self-efficacy beliefs of Turkish pre-service chemistry teachers. For this purpose, the College Chemistry Selfefficacy Scale (CCSS) was administered to 20 pre-service chemistry teachers. Then, phenomenological approach was employed and semi-structured interviews were conducted with five pre-service teachers selected based on their scores on the CCSS to identify the underlying sources. The emerging meanings and self-reported sources of participants' chemistry self-efficacy beliefs were analysed according to Bandura's sources of self-efficacy. Results indicated that mastery experiences were the major source of self-efficacy beliefs, supporting the tenets of social cognitive theory. Physiological arousal and vicarious experience were also influential but they were not as frequently reported as mastery experiences.