<jats:sec><jats:title>Background:</jats:title><jats:p>The genus<jats:italic>Deinococcus</jats:italic>consists of species in rod-shape (<jats:italic>Bacilli</jats:italic>) and spherical shape (<jats:italic>Cocci</jats:italic>).</jats:p></jats:sec><jats:sec><jats:title>Objective:</jats:title><jats:p>In this study, we aimed to determine whether the common ancestor of<jats:italic>Deinococcus</jats:italic>species was rod-shaped or spherical.</jats:p></jats:sec><jats:sec><jats:title>Methods:</jats:title><jats:p>We compared the homologs of the proteins related to the rod-shape in bacteria (MreB, MreC, MreD, MrdA, RodA, and RodZ) in various<jats:italic>Deinococcus</jats:italic>species and<jats:italic>Thermus thermophilus</jats:italic>.</jats:p></jats:sec><jats:sec><jats:title>Results:</jats:title><jats:p>The phylogenetic trees based on each protein and the homologs reflected the evolutionary relationships of the species, indicating that the Horizontal transfer of the genes did not occur during the<jats:italic>Deinococcus</jats:italic>evolution.</jats:p></jats:sec><jats:sec><jats:title>Conclusion:</jats:title><jats:p>The ancestor of the genus<jats:italic>Deinococcus</jats:italic>was rod-shaped, and the spherical forms appeared when the rod-shaped formation system was lost during evolution and diversification within the genus.</jats:p></jats:sec>