<p>This study was conducted to investigate the impact of the large-scale educational reform 2018 on teacher emotions in Vietnamese secondary education. A mixed methods approach was employed with an explanatory sequential design, utilizing a self-developed and validated survey questionnaire and semi-structured interviews. A total of 564 lower secondary and upper secondary teachers who were teaching subjects in the new curriculum participated in the study, with 21 of them interviewed later. The findings revealed that teachers experienced both positive and negative emotions; however, positive emotions were more prevalent and stronger than negative ones. Teachers expressed interest and curiosity about new teaching methods and were grateful for the reform as it provided professional development opportunities. However, they reported feelings of anxiety and confusion regarding the effective implementation of the reform. Teachers believed that the reform positively influenced their pedagogical knowledge and skills, and they acknowledged that it brought significant changes to the education system. Based on these findings, the study offers several implications for teachers and relevant stakeholders regarding teacher education.</p>