<p>Since the recognition of mercury as a global pollutant, studies have aimed to provide information on its biogeochemical trends and risks to humans and the environment. Mostly focused on aquatic matrices, mercury biomagnification studies have indicated sensitive populations and trends to mercury in the environment. Nonetheless there is still an information gap on mercury behavior in terrestrial ecosystems, especially those located in tropical developing countries. Due to its relevance to biodiversity conservation, tropical high-altitude grasslands, located in the Atlantic Forest, represent a great opportunity to study mercury’s behavior on mountainous sites. Thus, the main goals of this study were: to determine the occurrence of total mercury in high-altitude small mammals in Brazil, evaluating morphometric parameters, genus, sex and spatial variations over Hg bioaccumulation dynamics; to measure δ¹³C and δ¹⁵N stable isotopic values in biologic tissues as tool to understand the role of ecological interactions and their influence of Hg in food webs; and to assess the potential of Hg biomagnification in tropical high-altitude small mammal food webs. To achieve these aims, sampling campaigns were carried out at Itatiaia and Serra dos Órgãos National Parks (SE Brazil), collecting small mammal species in <i>campos de altitude</i> and cloud forest systems. For total mercury quantification, a CvAAS and, for (carbon and nitrogen) stable isotope measurements, an ICP-MS were used. We found mercury concentrations ranging from 12.5 to 2022&#xa0;μg/kg, δ¹⁵N ranging from 1.61 to 7.02‰ and δ¹³C ranging from −27.30 to −10.45‰ and TMS values of: 0.65 for Serra dos Órgãos National Park and 0.39 for Itatiaia National Park. The present work provides an initial screen of mercury in Brazilian tropical uplands vertebrates and its mobility through the food web. This is the first report of mercury biomagnification in terrestrial mammals in Brazil.</p>