This study provides a list of freshwater fishes of the Parque Nacional da Serra dos Órgãos (PARNASO; Rio de Janeiro state, Brazil) and its surrounding areas. Fish samplings were performed by electrofishing during the dry season (2010 –2011) in three different areas: 1, inside of the PARNASO (2 sites); 2, in the buffer zone (4 sites); and 3, in adjacent areas (8 sites). A total of 47 fish species in 13 families and six orders were recorded. Fish composition within the limits of the PARNASO differed from that recorded in the adjacent area, with the latter having comparatively higher species richness. The buffer area had intermediate ichthyofauna composition between the two other areas. This study enhanced knowledge on the composition and structure of the fish assemblages in PARNASO, by recording the occurrence of six new species within the park that were not included in the Management Plan of this Conservation Unit.