Online language learning with virtual classrooms (OLLVC) is becoming a reality to a large number of students across contexts. Yet students' motivation and engagement in OLLVC remains underexplored. The current study evaluated 6364 university students' motivation and engagement in OLLVC and its interrelationships with environmental support, learner attitude and readiness in the Chinese higher education context. This study employed the adapted motivation and engagement scale and adopted purposive sampling to recruit a sample of undergraduate students, who were engaged in online English learning using VC. The data were examined using structural equation modeling via Mplus 7.4. Results showed that students were generally motivated and engaged in OLLVC and there were significant individual differences across age, English proficiency, gender, academic ranking, and major. Moreover, student evaluation of their readiness for OLLVC mediated the relationships between support and attitude for online learning and student motivation and engagement in OLLVC. These findings call for attention to the importance of taking student readiness as a mediating mechanism in students' motivation and engagement in OLLVC. Implications for supporting virtual-classroom-mediated online language learning are also discussed.