The paper presents data referring to the comparative structure of the benthic invertebrate fauna of the Doamnei River, in the sector Cernat – Dârmăneşti. In all sampling stations, the main elements specific to unpolluted mountain waters are constantly present: amphipods, ephemeropterans, plecopterans, trichopterans, simuliids, 103 chironomids, most of them being dominant groups. On the basis of relative abundance, the dominancy of the invertebrate groups is highlighted. In particular, the community structure of the mayflies larvae (group constantly dominant in all studied sites) is analyzed, being presented the list of the taxa, ecological spectrum, relative abundance, frequency and other ecological characteristics of the mayflies fauna.