The study is aimed at investigating whether learning readiness contributes to university students’ group discussion in English in a flipped classroom. The research questions are: 1) Is there a change in learning readiness before and after flipped learning?; 2) Is there a change in students’ participation in group discussion before and after flipped learning?; and 3) Does learning readiness contribute to participation in group discussion? A total of 52 students participated in the study. Student survey questionnaires and quizzes were collected for data analysis. Wilcoxon matched pairs signed rank test, a non-parametric test for repeated measures t-test, and multiple regression analysis were utilized to answer the research questions. The statistical analyses produced the following results: 1) there was a significant change in students’ participation in learning readiness and group discussion; and 2) learning readiness and quizzes greatly contributed to group discussion. These findings corroborated the previous research that learning readiness is essential for self-directed learning in a successful flipped classroom. This suggests that teachers devise ways to help students engage in online activities for greater learning readiness.