There has been a continuous debate over a long period over the issue of using the learner’s mother tongue in teaching the second language. We have two schools in this regard – monolingual approach and bilingual approach. Those advocating the monolingual approach have claimed that learning is determined by the quantity of exposure to the target language. On the other hand, bilingual approach focuses on the fact that learners are facilitated by the use of their mother tongue. The primary concern of this study is to find out whether Bangla is used in teaching English at tertiary level in Bangladesh and if used, in which situation and to what extent. This study has been done in a private university situated in Dhaka. The researchers have used various techniques to collect the data, the analysis of which reveals that teachers of tertiary level use Bangla in English language teaching classes in some specific situations such as explaining difficult grammatical rules, presenting new vocabulary, giving instructions, etc. and they do so in accordance to the proficiency level of the learners.