This study aims to investigate the motivation and career interest in STEM fields of high school students enrolled in public schools in the districts of Kayseri in Turkey according to various factors, to ascertain the relationship between the two variables, and to present a model for the relationship between the variables. The causal-comparative research and correlation (relational) research designs, which are among the quantitative research designs, were used in this study, which involved 1,667 students from five high education institutions situated. The research employed the Career Interest Scale in STEM Fields and the Motivation Scale in STEM Fields to gather data. It has been found that students whose favorite and most successful course is about STEM have much higher motivation and career interest in STEM fields than the other pupils. According to the study, students who are considering majoring in one of the university’s STEM fields have much higher motivation and career interest in STEM fields than other students do in general. Additionally, the connection between motivation and career interest in STEM fields was looked at. According to research, students’ motivation in STEM fields accounts for 70% of changes in their career interests in those fields.