English as a medium of instruction (EMI) is currently a trend for non-English courses. It is also implemented in various universities in Indonesia. However, Indonesian as the first language (L1) still exists in EMI implementation. It is used to make students understand. On one hand, teachers are ready to use EMI, but, on the other, students ask for the use of L1 because they have limited English competency, which impacts their understanding the English instruction. This research aims to investigate students' and teachers' perceptions and the implementation of EMI in the Biology study programme at a private university in Bali, Indonesia. EMI is used in delivering course content by the content teachers. A case study design was utilised for the current research. Forty students experienced EMI in the plant physiology course and two content teachers were considered as the subjects of the study. Data were collected by document study, observation, employing questionnaires, and interviews. The result showed that teachers and students agreed on the importance of using EMI with the use of L1 even though it impacts feelings of difficulty and anxiety. As such, Biology students have to be provided with intensive English courses, English for Biology terms, and Biology materials are written in English to enhance their English language skills both in written and oral communication.