G12 group A rotavirus (RVA) are currently recognized as a globally emerging genotype and have been described in combination with several P-types. In Brazil, G12 RVA strains have been described in the Southern (2003) and Northern (2008–2010) regions, in combination with the P[9] and P[6] genotype, respectively. To date, few complete genomes of G12 RVA strains have been described (none from Brazilian strains), considering G12P[9] genotype just one strain, RVA/Human-tc/THA/T152/1998/G12P[9], has their 11 gene segments characterized. This study aims to determine the genomic constellation of G12P[9] and G12P[8] RVA strains detected in Brazil between 2006 and 2011. Therefore, the eleven gene segments of five Brazilian G12 RVA strains were amplified and sequenced, and the genotype of each gene segment was assigned using phylogenetic analysis. Complete genome analyses of G12 RVA strain circulating between 2006 and 2011 in Brazil revealed a conserved Wa-like genomic constellation for three G12P[8] RVA strains; whereas the two G12P[9] strains possessed distinct reassorted AU-1-like genomic constellations, closely related to the reference strain RVA/Human-tc/THA/T152/1998/G12P[9] in most genes. The results obtained in the current study suggest that G12P[9] (AU-1-like) and G12P[8] (Wa-like) strains detected in different regions of Brazil do not share a common origin. Moreover, while Brazilian G12P[8] RVA strains showed a complete Wa-like human constellation, both G12P[9] strains possessed an NSP1 gene of bovine origin (NSP1), and RVA/Human-wt/BRA/PE18974/2010/G12P[9] also possessed a VP3 gene of canine/feline origin.