Antarctic microorganisms are characterized for living under extreme conditions such as low temperatures, and high UV-radiation, including and freeze-thaw stress derived from annual environmental changes. Microbial mats are successful microbial consortia in these extreme environments, yet much is unknown regarding their diversity and functional role in terrestrial polar regions. The bacterial diversity in microbial mats from Fildes Peninsula in Maritime Antarctica and their genetic potential for nitrogen acquisition has been explored in our laboratory. The results showed that microbial mats were clustered within two main groups according to their 16S rRNA genetic diversity, separating those collected nearby scientific stations from those in coastal plains. The later showed a lower relative proportion of Proteobacteria and a higher proportion of Cyanobacteria, Planctomycetes, and Thaumarchaeota, possibly due to physicochemical and biological factors associated with sea-land interactions. All microbial mats had a strong nifH genetic signal, mainly associated with Cyanobacteria and Proteobacteria, suggesting the relevance of both oxygenic and anoxygenic bacteria potentially involved in N-fixation. The capacity of Oscillatoriales and Acaryochloris marina to assimilate Nitrogen was also evidenced. This study showed the diversity and structure of microbial mats in the Fildes Peninsula and the importance of cyanobacteria in microbial mats based on their role for N2 fixation and N- assimilation.