The aim of this study is to identify prospective secondary mathematics teachers' opinions about the mathematical modeling method and the applicability of this method in high schools. The case study design, which is among the qualitative research methods, was used in the study. The study was conducted with six prospective secondary mathematics teachers who were taking a "teaching practice" course. In the "Teaching Practice" course, mathematical modeling method was introduced to these selected prospective teachers and activity examples appropriate to this method were presented to them. Then, the prospective teachers prepared examples similar to the activity examples that were presented to them, and they implemented these examples in the schools where they served their internship. The semi-structured interview and observation forms were used as data collection tools in the study. An attempt was made to identify prospective secondary mathematics teachers' opinions about mathematical modeling method and the applicability of this method via interviews, whereas an attempt was made to identify their efficacy in application the mathematical modeling method via observations. Descriptive analysis and content analysis methods were used in analyzing the data. In view of the study, it was found that many of the prospective teachers correctly understood what mathematical modeling meant, but they were not able to fully implement this method in classrooms. When the prospective teachers' opinions about classroom applications of the mathematical modeling method were examined, it was observed that the reasons for the experienced difficults are the fact that there was not enough time and classroom management was difficult. As for the positive aspects of mathematical modeling, the prospective teachers stated that the mathematical modeling set forth the applicability of mathematics in daily life. Furthermore, all prospective teachers stated that they consider featuring problems that involve this method in their own courses in the future, but some of them stated that they would not be able to use it since its application is difficult and time consuming.