This research investigates the effect of individual voice training on pre-service Turkish language teachers' speaking skills. The main claim in this research is that teachers' most significant teaching instrument is their voice and it needs to be trained. The research was based on the convergent parallel mixed method. The quantitative part was carried out according to the changing criterion model, which is a single subject design. In the qualitative part, the data were obtained from semi-structured interviews conducted before and after the intervention phase and the diaries kept throughout the process. Three pre-service Turkish language teachers, voluntarily participated in the study. First, the baseline level of the participants was determined, then the intervention phase was implemented accordingly (a five-week individual voice training). Each participant received one-hour individual voice training weekly, and three case evaluation sessions were conducted at intervals after each training session. At the end of five weeks, more than 90% improvement was recorded in all participants. Data analysis also revealed that their perceptions of self-efficacy increased and anxiety levels decreased in terms of public speaking. Finally, it is suggested that voice training need to be integrated into Turkish language teacher education program.