Background The Conserved Oligomeric Golgi (COG) complex is an eight-subunit assembly that localizes peripherally to Golgi membranes and is involved in retrograde vesicular trafficking. COG subunits are organized in two heterotrimeric groups, Cog2, -3, -4 and Cog5, -6, -7, linked by a dimeric group formed by Cog1 and Cog8. Dysfunction of COG complex in humans has been associated with new forms of Congenital Disorders of Glycosylation (CDG), therefore highlighting its essential role. In the present study, we intended to gain further insights into the evolution of COG subunits in vertebrates, using comparative analyses of all eight COG proteins. Results We used protein distances and dN/dS ratios as a measure of the rate of proteins evolution. The results showed that all COG subunits are evolving under strong purifying selection, although COG1 seems to evolve faster than the remaining proteins. In addition, we also tested the expression of COG genes in 20 human tissues, and demonstrate their ubiquitous nature. Conclusions COG complex has a critical role in Golgi structure and function, which, in turn, is involved in protein sorting and glycosylation. The results of this study suggest that COG subunits are evolutionary constrained to maintain the interactions between each other, as well with other partners involved in vesicular trafficking, in order to preserve both the integrity and function of the complex.