This study aims to describe the use of the Kutai Tenggarong language in elementary schools in Kutai Lama Village, Anggana District, Kutai Kartanegara Regency, East Kalimantan. This scientific study using descriptive qualitative research. Data collected from three sources: field information, learning activities in elementary schools, and supporting documents. The results of field research indicate that the Kutai Tenggarong language is still dominant in the learning process in elementary schools in Kutai Lama Village, Anggana District, Kutai Kartanegara Regency. The factors that influence include (1) there is no balance of formal language in the learning process in the classroom, (2) the habits of class teachers who often speak Kutai Tenggarong, and (3) the Kutai Tenggarong language, which attracts students' attention. The use of their mother tongue has an impact on their understanding of the formal language or Indonesian, which they should have known since elementary school.
Key words: Mother tongue, Kutai language, elementary school