A study on fish biodiversity was conducted in 2024 through two sampling campaigns at 22 sites along five watershed transects: Khe Choang, Khe Bu, Khe Kem, Khe Thoi, and Co Phat within Pu Mat National Park. One hundred thirty-nine species were recorded, belonging to 80 genera, 17 subfamilies, 28 families, and 11 orders. Among them, seven species are listed in the Vietnam Red Data Book (2024), including two classified as Endangered (EN): Anguilla marmorata and Poropuntius krempfi, and five classified as Vulnerable (VU): Altigena tonkinensis, Decorus lemassoni, Pseudohemiculter dispar, Hemibagrus guttatus, and Bagarius rutilus. The study also reported 29 species with newly identified distribution ranges and recognized 35 species of economic importance in the study area. These findings highlight the biodiversity richness and conservation significance of the ichthyofauna in Pu Mat National Park.