The general purpose of this research is to examine the mediating effect of STEM attitudes between STEM pedagogical content knowledge (CK) and STEM intra-class practice self-efficacy. This research was conducted in a causal design. A total of 345 teacher candidates, 261 females (75.7%) and 84 males (24.3%), were included in the research. The data were collected with the STEM Pedagogical CK Scale (STEM), Attitude Scale for STEM Education (STEMAS), and STEM Intra Class Practice Self-Efficacy Perceptions Scale. Path analysis technique was used in data analysis. In addition, bootstrapping analysis was used to evaluate the significance of the mediating effect of STEM attitudes. At this point, 1,000 resamples were made and lower-upper bound confidence intervals were determined. In research results, the mediating effect of STEM Attitudes was found to be significant in the relationship between STEM Pedagogical CK and STEM Intra Class Practice self-efficacy.