Tropical forests are the most biodiverse ecosystems on Earth. Unfortunately, they are often degraded by large enterprises that convert large areas of continuous forest into forest mosaics or into deforested areas in order to seek economic development through infrastructure construction. This study evaluates how the assemblage of nonvolant small mammals is structured after the implementation of a bauxite mining in the Saracá-Taquera National Forest, Pará, Brazil. We tested the hypothesis that the clearings for bauxite mining produce an edge effect over the small mammal assemblage and that the size of the deforested area increases the impact’s magnitude. Data collection took place through live traps from 2010 to 2012, totaling an effort of 56,220 trap nights in both impacted and pristine areas. Generalized Linear Models revealed that the size of the mined area was the main predictor explaining species impoverishment in impacted areas. Multivariate Permutational Analysis of Variance and Multivariate Dispersion Permutation Analysis revealed differences in species composition between impacted and nonimpacted sites and that these differences are due to species turnover. We recommended that concessions for land use should be rethought, especially in protected areas and when major areas are subjected to a new economic exploitation cycle.