Camera-trap surveys were carried out at two different sites within the Atlantic Forest of Misiones province, Argentina, to study the density, habitat use and activity patterns of ocelots. At Urugua-í Provincial Park, 17 different individuals were captured (nine females, six males, two of unknown sex) during a 3-month-long survey (34 camera stations, 1409 trap days). At Iguazú National Park, 34 different individuals were trapped (20 adult females, nine adult males, two subadult females and three of unknown sex) during the survey (39 sampling stations, 1631 trap days). Population density estimates (±se) for Urugua-í, in an area of between 150 and 259 km2 (depending on the buffer used to estimate the area effectively sampled), range from 7.7±1.4 to 13.4±2.6 individuals × 100 km−2, whereas at Iguazú, in an area of between 275 and 428 km2, a population density of between 12.8±2.7 and 20.0±4.2 individuals × 100 km−2 was estimated. Minimum observed range estimates for individuals with >3 capture sites range from 3.19 to 37.09 km2 for four males and from 4.17 to 7.11 km2 for three females, but underestimate the true home range size. Ocelots were captured more frequently along old roads than on new trails opened with machetes. Ocelots were captured more frequently at night than during the day and reduce their use of roads and trails during the week previous to and during full moon nights, a behavior previously reported for Amazonian ocelots. Population density estimates for ocelots in the Upper Paraná Atlantic Forest ecoregion are lower than those at other neotropical sites. The whole Green Corridor contains a population of about 1280 individuals. This estimate should bring our attention to the larger cats (pumas and jaguars) that live at lower population densities because the future of their local populations is compromised if protected areas are not urgently created and properly managed.