The increase in Protected Areas (PA) at a global scale during the second half of the 20th century reflects the growing concern for preserving lands in the face of biodiversity and habitat loss. However, in most cases, there is no clear evidence for PA effectiveness. Nahuel-Huapi National Park is the first and biggest Argentinian PA (750,000 ha); it hosts few large and medium size mammal species; however, the diversity of small mammals equals those found in temperate forests elsewhere. Our goal was to evaluate the conservation status of the small mammal communities in the Nahuel-Huapi protection system, accounting for the three different PA categories. To this end, we established five plots of 60x60 m in each level of protection (Strict-Natural-Reserve, National-Park, National-Reserve, outside PA), setting 50 traps per plot, over four consecutive nights monthly, during summer 2015 and 2016. Capture effort was 41,600 trap-days. We identified eight species: Abrothrix hirta, A. olivacea, Oligoryzomys longicaudatus, Geoxus valdivianus, Chelemys macronix, Irenomys tarsalis, Loxodontomys micropus, Dromiciops gliroides. We marked and released each individual, resulting in 727 (in 2015) and 532 (in 2016) individuals (10.2 % and 9.02% capture success respectively). We compared species richness, Shannon-Wiener diversity-index, and abundance between the four levels by ANOVA. Total abundance was higher in the highest level of protection for both seasons; however, the unequal abundance and distribution of small mammals across the 20 plots requires a more detailed study in order to elucidate if this heterogeneity is inherent to the group or to the protection system itself.