Background Study: As flipped learning is a flexible pedagogical methodology to tailor students' needs and maximize the learning effects, this study integrated peer learning with MosoTeach‐supported flipped mode in an undergraduate blended EFL course. MosoTeach is a popular online learning platform in China with a variety of learning resources. Objectives: The study aimed to test the impact of MosoTeach flipped learning (MTFL) mode on undergraduate EFL students' perceived motivation, participation, feedback, and test performance. Methods: A quasi‐experimental design was carried out in Z university during the spring semester of 2020, with the experimental group (n = 34) adopting the MTFL model and a control group (n = 33) the non‐flipped mode. Results and Conclusions: The independent t‐test results showed that the experimental MTFL group outperformed the control group in post‐test scores, and a positive correlation was found in the relationship between the experimental MTFL group's post‐test scores and MosoTeach learning experience points (LEPs). Moreover, the course perception questionnaire survey indicated a higher level of students' perceived motivation, participation, and feedback in the experimental MTFL group, which corresponded to the results of the content analysis of students' responses to open‐ended questions and reflective reports. But students in both groups experienced challenges such as isolation, procrastination and technological anxiety. Lay Description: What is currently known about this topicFlipped language learning is mostly reported to be effective in improving EFL learning.Peer learning is mostly reported to be effective in improving EFL learning.MosoTeach was investigated in English learning contexts before, but without experimental design. What this paper addsMosoTeach proved as a valid online learning platform in flipped language learning, and the learning experience points (LEPs) on MosoTeach could predict students' exam performance.Students in the experimental group (MosoTeach‐supported flipped) had better exam performance and a higher level of motivation, participation and feedback.Students in both groups experienced isolation, procrastination and technological anxiety. Implications for practice:Peer discussion boards in MosoTeach provide learning support effectively for students in pre‐class learning.Group projects and peer assessment in MosoTeach integrate pre‐class peer discussion into in‐class interaction successfully.MosoTeach provides equal opportunity for every student in the large‐size Chinese English classes, thus contributing to the equity of in‐class peer interactions. [ABSTRACT FROM AUTHOR]