In order to perform environmental impact assessment on Jangheung Dam construction, we investigated fish fauna and community from February to November 2005. Fishes were collected seasonally in 3 sites at upstream and 5 sites at downstream of the dam using cast net and kick net. A total number of fish caught from the study area was 8,733 fish representing 15 families and 45 species, and Cyprinidae and Gobiidae Families had twenty-four (53.3%) and four (8.9%) species, respectively. However, rest of families composed of one to three species. There was the 2nd-class endangered species, Sand lamprey (Lampetra reissneri), found in the upstream (Site 3) of the dam, and fourteen Korean endemic species (31.1%) including southern king spine loach (Iksookimia hugowolfeldi). In the mean time, one foreign introduced species, Crucian carp. (Carassius cuvieri) was mostly found in upstream of the dam among the 45 species. The number of species in each site ranged 20 to 34 species, and it tended to increase toward to downstream. The species of pale chub (Zacco platypus, 43.5% relative abundance) and dark chub (Zacco temminckii, 14.7%) were dominant and subdominant species, and 14 species including eel (Anguilla japonica) comprised less than 0.1% relative abundance (rare species) of the total catch. Compared to assessments in previous years (1998~2004), the number of species found in 2005 was the maximum. Fifteen species were not confirmed at this year even if they were found in previous years, and some of them including hickory shad (Konosirus punctatus) were peripheral species of fish collected in only single year. Whereas three species (Lampetra reissneri, Carassius cuvieri, Hemiculter eigenmanni) was confirmed for the first time in 2005. Based on the results, modification of fish fauna and community in Tamjin River watershed should be monitored in detail in order to assess any negative effect due to dam construction, and additional investigation for the endangered species needs to be performed to establish conservation of their habitat and population.