The aim of this study is to apply flipped learning in teaching General English courses in university and examine its impact on English self-efficacy and students’ English achievement. The researcher implemented flipped learning by recording videos based on the students’ textbook and up-loading those videos on the SNS before each lesson to provide opportunities for active interactions in class. The students of the experimental group (n=56) were required to learn through SNS the videos to learn in the pre-class. They also practiced what they had learned under the teacher’s supervision by completing collaborative tasks in groups or pairs. Meanwhile, the control group students (n=66) received in-class only traditional English teaching. The statistical analysis of the results showed that adopting the flipped learning strategy appeared to play a role in enhancing the students’ English self-efficacy and English achievement. Also the students’ responses indicated that their satisfaction towards the flipped learning is positive.