This research aimed to analyze the mood systems realized on Lecturer-students’ Interaction in Teaching-Learning Process on Whatsapp Group, to explain the contributions of the lecturer students’ interaction towards the teaching discourse analysis and the significances and implications of the teaching-learning process through WhatsApp Group. This research used a qualitative approach by applying discourse analysis proposed by Halliday and descriptive research design to gain rich data about particular phenomenon during the Covid-19 Pandemic. The subject of the research was one of the lecturers and the students of English Department. The data source used in this research is the data transcriptions from the transcript of the lecturer students interaction on WhatsApp Group. First, the data analyzed by using mood element analysis. Second, the analysis is based on the mood type, either indicative, interrogative, imperative, or exclamative mood. After that, the researcher found the dominant mood system appeared on the lecturer and students interaction. The result of data analysis showed that there are 211 clauses of lecturer-students’ interaction analyzed. The dominant mood system of lecturer students interaction in the research subject was declarative mood as it got 72.5%. As the declarative mood was closely related with statement in the speech functions, it means that the clauses in lecturer-students’ exchange are successful functioned as statements to give as much information to the participants Besides, the contribution of lecturer students mood analysis contributes the teaching discourse analysis, and the significances and implication of using WhatsApp Group can increase student motivation to follow the learning process.