Although recent years have seen a growing interest in students' experiences of boredom in foreign language learning, scant attention has been paid to this negative emotion in online live classes. With a mixed-methods approach, this study investigated what factors were responsible for student boredom in online live classes and what made Chinese students majoring in English more bored in online live classes than in traditional in-person classes. Data were collected through a questionnaire and focus group interviews. Quantitative and qualitative data analyses revealed that the main factors responsible for this negative emotion in online live settings were teacher-centered classes, less engagement and interaction, high task challenges, monotonous and long learning activities, textbook-based activities, students' lack of self-discipline, peer influences, the absence of emotional support, unreliable internet connection, physical fatigue, a locked-down campus, and a dormitory learning environment. Students' greater boredom in online live settings than in-person settings arose from student-related factors, technological factors, and environment-related factors. This study sheds light on how to alleviate student boredom in foreign language learning in online live settings. Plain language summary: With a mixed-methods approach, this study aimed to investigate what factors were responsible for student boredom in online live classes and what made EFL students more bored in online live classes than in traditional in-person classes. Data were collected through a questionnaire and focus group interviews. Quantitative and qualitative data analyses revealed that the main factors responsible for this negative emotion in online live settings were teacher-centered classes, less engagement and interaction, high task challenges, monotonous and long learning activities, textbook-based activities, students' lack of self-discipline, peer influences, the absence of emotional support, unreliable internet connection, physical fatigue, a locked-down campus, and a dormitory learning environment. Students' greater boredom in online live settings than offline settings arose from student-related factors, technological factors, and environment-related factors. The findings in this study have implications for practitioners seeking to alleviate this negative feeling in online live classes. To enhance the effectiveness of online live learning, it is important for instructors to provide timely emotional support for students, create a good learning environment, design more interactive activities, change teacher-centered classes into student-centered classes, avoid monotony in teaching methods, design tasks based on students' needs, decrease screen time, etc. The study has two limitations. First, the sample size was relatively small, which might limit the generalizability of the results. Second, the data were collected at the end of the semester, with students recalling their experience, which might overlook their immediate instances of boredom and their dynamic change of this negative emotion. [ABSTRACT FROM AUTHOR]