The Kayan River is the longest in North Kalimantan, inhabited by various types of aquatic biota. However, in recent times there have been established multi-national oil palm plantations and mining around the Kayan River which will have an impact on the Kayan River ecosystem. The aim of this study is to determine the ecological status of the Kayan River based on current conditions. Fish sampling is carried out along the Kayan River starting from the upper reaches of the Bahau River to the downstream. Identification of fish is based on the Fishbase Organization, FAO and Kottelat. Measurement of water discharge using the SNI 8066: 2015 method, Total Suspended Solid refers to SNI 06-6989.3-2004. Determination of species diversity using the Shannon-Wiener Index, while the measurement of dominance index uses the Simson Index. The results obtained 37 species from 16 families during the 2019-2020. The family of Cyprinidae is the largest fund with 32%. Among the 37 species found 9 native species of Kalimantan, 3 invasive species, 1 species of saltwater fish, and 2 species of fish are included in the IUCN red list. Fish that are included in the endemic/native category of the Kayan River are Anguilla borneensis, Hemibagrus capitulum, Nematabramis alettes borneensis, Clupeoides borneensis and Osphrenemus septemfaciatus, and Pangasius rheophilus. Based on the results of the study, it can be concluded that the ecological status of the Kayan River fish is still considered very good and stable during the research period.