We discuss the students' knowledge of their ethnomathematics. This research is a case study on elementary school students in Pegunungan Arfak of West Papua using ethnographic methods. The results obtained that ethnomathematics is the result of human thought within the culture, but its users are sometimes unaware. Therefore, ethnomathematics is a doing mathematics in the culture. Associated with ethnomathematics-based learning, students need to be introduced or made aware of their ethnomathematics.