STEM education is an important approach for preparing students for a competitive workforce with essential skills in the 21st century. However, successfully implementing STEM education in primary and secondary schools presents a variety of challenges. The study suggests that a neglected challenge in the literature is how to sustain teachers’ positive emotions toward STEM educational work, which may cause teachers to be more engaged in, motived by, and committed to STEM education. Therefore, the study aims to contribute to the literature by investigating the mechanism of the construction and suitability of teachers’ emotions toward STEM educational work based on a single case study conducted in Hong Kong from the social constructionist perspective. The major findings of the study indicate that (1) positive emotions toward STEM educational work may be constructed by the teacher’s positive interpretation of the work, i.e., STEM educational work as the facilitator of students’ overall development and that (2) positive emotions toward STEM educational work may be sustained by enabling school institutions to have the elements of shared power, administrative support, and the value of a whole-person education. Copyright © 2021 MDPI AG