It has been widely agreed that the approaches teachers apply to language teaching, the attitudes students have, their motivation and target language proficiency are directly influenced or determined by their beliefs about language teaching and language learning respectively. This paper reports on a study which explored Mongolian teacher, Han teacher and Mongolian learner beliefs about the English teaching and learning of Inner Mongolian university students, with particular focus on the students' second language ability, the languages for classroom instruction and materials development. The results of the study indicate that there are belief differences among teachers and students; in particular, the beliefs of the Han teachers differ from those of Mongolian students. This study concludes that in order to improve Mongolian students' English teaching and learning, it is of vital importance to fill the belief discrepancy between teachers and students with regard to L3 acquisition, which is regarded as one of the crucial factors influencing the teaching and learning of English for Mongolian students in multilingual contexts in Inner Mongolia, China.