Math is required for students in order to have mathematical communication skills. This research was aimed to analyze the students' mathematical communication skill on trigonometric material. This research utilized a qualitative approach in the form of a case study. There were six students from science major as the subject of the research. The data collection technique utilized tests and interviews. The data analysis techniques were conducted by data reduction, presentation of data, and drawing conclusion/verification. The research finding presented that the students' mathematical communication skill is deficient. The causative factor because which some students can not hook real objects, pictures, and diagrams into mathematical ideas, inappropriate symbols used and explain the mathematical model perfectly. Students made types of mistakes such as adversity in communicating the mathematical model, misunderstanding about the questions and wrong variable concept used.