Recently, flipped classroom approach has received much attention from teachers of different subjects around the world. This new pedagogical model has been reported to be a potential method in the area of EFL teaching. In Viet Nam, teaching English grammar has mainly focused on students’ acquisition of grammar rules without much practical application in real communicative situations. This case study aims at investigating the affordances faced by students in a flipped English grammar class in order to help language teachers to harness the approach to enhance their students’ learning. Qualitative research design was adopted in the study. Thirty four students majoring in the English language at a university in Viet Nam attended a 10-week flipped grammar class. The instruments included the semi-structured interviews with ten students randomly selected from the participants. Thematic analysis was performed to address the qualitative data drawing on the Activity Theory framework. Twelve affordances of the flipped classroom approach in English grammar instruction such as being self-paced in learning, offering opportunities to voice opinions, saving time for in-class communicative activities and facilitating learning English grammar communicatively were identified. The results of the study offer valuable implications for the application of this model in teaching English as a foreign language, especially in the context of Viet Nam.