Scientific reasoning competencies (SRC) are an area of competence emphasized in science education and are considered essential in the world of 21st Century skills. Developing these competencies is important for all levels of education, from primary school to university. However, to accurately measure them, measurement tools with validity and reliable evidence are needed. The current study was conducted with two different sample groups. In Study-1 (n = 155), the SRC test consisting of 21 items was adapted into Turkish, and evidence of its validity and reliability was presented. To this end, the Turkish adaptation of the SRC test, which was previously developed and tested for validity in different languages, was conducted in a sample of primary school teacher candidates. In Study-2 (n = 483), the relationship between SRC and epistemological beliefs and analytic thinking skills was examined. Regression analysis showed that epistemological beliefs and analytic thinking were significant predictors of SRC. The study and discussion offer implications for future research on the relationship between SRC and other thinking skills not examined in this research.