We performed field investigations at six stations in Buk Stream of Goseong-gun, Gangwon-do, Korea, from May to September 2009 to understand the stream`s fish fauna and community structure. In the survey, 31 species belonging to 20 families were collected. Dominant species by number was Zacoo koreanus(30.0%), and subdominant species were Pungitius kaibarae(9.4%) and Rhynchocypris steindachneri(9.3%). In biomass, the dominant species was Tribolodon hakonensis(35.5%), and subdominant species were Z. koreanus(22.5%) and Cobitis pacifica(7.5%). Eight Korean endemic fish species and two endangered species (P. kaibarae and Pungitius sinensis) were collected. In addition, four anadromous fish species (T. hakonensis, Oncorhynchus masou masou, O. keta, Gasterosteus aculeatus) and two amphidromus fish species (Plecoglossus altivelis altivelis and Gymnogobius urotaenia) were observed. Interestingly, we verified the existence of several fish species in Buk Stream where they have not lived before. Those species were previously reported to live only in rivers that run into the western and southern sea of Korea. Five of those species (Zacoo koreanus, Z. platypus, Silurus microdorsalis, Liobagrus andersoni and Coreoperca herzi) were reported in Buk Stream in the 1980s. The other species (Pungtungia herzi, Pseudorasbora parva, Squalidus multimaculatus, Misgurnus mizolepis, Koreocobitis rotundicaudata, Silurus asotus and Odontobutis interrupta) have been introduced since the 1990s.