UDK 574.587:595.371(497.6 Sarajevo)          595.371:502.17(497.6 Sarajevo) The paper is the result of a research into the composition of benthos of the hydro-system within the protected area of Vrelo Bosne (water source of River Bosna) and the wider region during 2009 - 2010 period. The aim of the paper is to establish the state of the populations of the endemic species of amphipod Niphargus illidzensis S., get an overview of the underlying ecological conditions within the habitats, conduct a morpho-metrical analysis of the specimens and designate the new habitats of this species. By analysing the basic physical/chemical and biological (phytobenthos and macrozoobenthos) parameters a high-quality level of water inside the habitats of this endemic species of amphipods was established: the water source of River Bosna (four), stream Stojčevac and the water source in the area of Blažuj. The highest number of specimen was recorded in stream Stojčevac where the longest specimen was also noted – 22 mm. The source in the area of Blažuj (potable water bottling plant Dijamant) is the new habitat for this species which was previously only noted in the area of Avala and Topčider near Belgrade. The paper presents a comprehensive overview of the ecology and the current state of this endemic species after its repeated description dating from 1974.