Teacher professional diaries are teacher reflections on their own and their colleagues’ observed practice. They are effective tools of increasing teacher qualification. Few research studies worldwide, while no such research studies in Georgia have been conducted on the impact of the application of reflective diaries on teachers’ reflective, communicative, and professional skills. Therefore, the aim of the research was to find out whether teachers’ reflective, communicative, and professional skills developed as a result of the application of reflective diaries, and if so, to what degree they increased. Quantitative research (an experiment with participation of 62 teachers) was held, with an experimental group whose participants wrote reflective diaries for 9 weeks and a control group which did not undergo any special treatment. A 5-point Likert scale questionnaire was developed, and its reliability and validity were assessed. Pre-experimental and post-experimental self-assessment questionnaire was held, the results were assessed and compared through descriptive statistics and a T-test. The results revealed that there was a positive average relationship between the application of diaries and reflective thinking, communicative and professional skills. According to the study results, the application of teacher reflective diary can be recommended as an effective tool for the development of reflective thinking, communication, and professional qualification. Keywords: communicative skills, professional skills; reflection diary, reflective thinking skills