This study investigated the relationship among adult affective factors, engagement in science, and scientific competencies. Probability proportional to size sampling was used to select 504 participants between the ages of 18 and 70 years. Data were collected through individual face-to-face interviews. The results of hierarchical regression analysis showed that while controlling demographic variable factors, science-related affective factors held explanatory power for scientific competencies. Among those factors, the explanatory power of self-efficacy was the greatest, followed by enjoyment and interest in science. While controlling antecedent factors, engagement in science held explanatory power for scientific competencies. It is suggested that improving affective factors and engagement in science may enhance adult scientific competencies. In terms of adult education, this study suggests that with more accessible science resources, adults may have the potential to trigger their interest, increase their self-confidence, and engage themselves in scientific issues.