This study aimed to identify structural relationships among variables by examining the direct and indirect effects of cognitive factors such as self-regulated learning strategy and definitional factors such as attitude toward science and scientific self-efficacy on science core competency in middle school students. To this end, the researcher examined the causal relationships among the variables using data from 438 students in all grades at S middle school in a metropolitan city. The results showed that middle school students' self-regulated learning strategy, attitude toward science, and scientific self-efficacy had a direct effect on science core competency, and that self-regulated learning strategy had a direct effect on attitude toward science and scientific self-efficacy. In addition, middle school students' self-regulated learning strategy had an indirect effect on science core competency through attitude toward science and scientific self-efficacy. Therefore, it is necessary to educate students from a comprehensive perspective that considers cognitive factors such as self-regulated learning strategy and defining factors such as attitude toward science and scientific self-efficacy in order to foster science core competency in middle school students.