The development of teacher education focusing on reflective practice as well as the study of pre-service teacher reflections are educational concerns. This research seeks to categorize the levels and the nature of pre-service Chemistry teachers' reflections in a public university in Southern Brazil. For this, autoscopies of the pre-service teachers' microteachings were conducted in a supervised internship discipline. Data were collected through an open questionnaire and with the autoscopies of their microteachings. The analytical procedures were performed according to Content Analysis, from which the results show that the pre-service teachers engaged in three distinct levels of reflection: technical descriptions, deliberate reflections and critical reflections when thinking about their own microteaching experiences. By analysing the nature of the reflections, six categories emerged; reflections on: class planning; their teaching; the objectives; personal aspects; the autoscopy; and the students. The research results showed a low incidence of critical reflections, presenting the possible difficulty pre-service teachers had in this level of reflection. The Reflective Intervention proved to be useful for promoting reflections of the three levels of reflection, especially level 2 reflections, which consists of deliberate reflections. The results and analyses of this study contribute to the research in reflective teacher education in science, specifically in regards to a greater understanding of the levels and nature of pre-service teachers' reflections and the use of reflective interventions as an approach to promote critical and deliberate reflections in science teacher education.