Although existing research has documented the significant relationship among student interest, engagement, and learning outcome, limited studies have investigated how adults’ interest and engagement in learning science are related to their scientific competency and environmental action. This study used 2012 and 2015 national datasets which were collected from face-to-face interviews representing how the interest and engagement of Taiwan citizens in understanding and exposure to science in society synergistically interact with their scientific competency and environmental action. Results showed that engagement in learning is more predictive to scientific competency and environmental action than interest. In addition, engagement in visiting science museums appears to be a superior venue for promoting adults’ environmental action than watching science related TV programs. These findings reveal an effective strategy of promoting adult environmental action through science communication and the importance of deep science learning.