The aim of this study is to examine pre-service mathematics teachers' views on reasoning, importance of reasoning in geometry and development of reasoning skills. The study was designed in the phenomenological (phenomenological) design, one of the qualitative research methods. The study group of the study was conducted on 61 pre-service teachers who were studying in the elementary school mathematics teaching program of a university in the Southeastern Anatolia region of Turkey. In the study, a semi-structured interview form, developed by the researcher to collect data, was used to determine the opinions of pre-service teachers on the reasoning, types of reasoning and the importance of reasoning skills in geometry. The data obtained through this form were analyzed by content analysis method. When the research results are examined; It was determined that the pre-service teachers did not have sufficient knowledge about reasoning and the components of reasoning skills. The pre-service teachers stated that reasoning skills are important in geometry. In addition, the pre-service teachers expressed important and valuable views on what can be done to improve reasoning skills. Suggestions are presented depending on the results of the study.