This study tested the psychometric properties of the "Sense of Belonging in STEM" Scale (SOB-STEM), a new scale measuring students' subjective evaluation of their academic and social experiences in STEM learning contexts, primarily focusing on purposeful interpersonal interactions. Data from 758 college students were analyzed, yielding several key results. Internal consistency reliability of the SOB-STEM was fairly strong (? = 0.801). Convergent validity was supported, with the SOB-STEM correlating moderately (r = 0.49, p < 0.01) with the "University Environment Scale." Implications for STEM teaching, program reform, and future research are discussed.