The opinions of mathematics teachers about using mathematical modeling (MM) in daily life problems and their use of MM in solving a daily life problem were examined within the scope of the graduate-level MM course in this study. The research was designed as a case study. Participants are five mathematics teachers selected by the purposive sampling method. The data were obtained through a structured form containing questions about a daily life problem and using MM in a daily life problem. Teachers were given one week to answer the questions on this form. Descriptive analysis was performed on the data obtained from the teachers' problem solving, and content analysis was carried out on the data containing the teachers' opinions. The findings determined that although the modeling processes were generally used appropriately by the teachers in solving a daily life problem, the process of understanding the problem was quickly mentioned, the teachers had difficulties in giving the most effective solution during the evaluation stage, and the communication stage was mostly ignored. It was also found out that MM could be beneficial in many ways in solving daily life problems. On the other hand, it was indicated that there may be difficulties in terms of student-teacher-environment and that teachers give very limited space to MM in classroom practices. It can be stated that the tendency of teachers to use the approaches they are accustomed to instead of MM in the solution of daily life problems is effective in the emergence of this situation.