Introduction: An effort to establish phylogenetic values for the major gamma-Aminobutyric acid A (GABA_A) receptor subunit mRNAs α, β, γ, δ, ε, θ, π could be improved our knowledge on their classification and function. In addition, the similarities and divergences between different species can be important to determine the function of these receptors. Materials and Methods: After alignment of mRNA complete gene sequences of GABA_A subunits in homosapinse and rattus norvegicus species, the phylogenetic tree were constructed with CLC Main Workbench 5.5 software. Results: The results revealed highly similarities between GABA_A subunits of homosapience and rattus norvegicus. In addition, these findings illustrated some divergences between β1, β2, β3, γ1, γ2, ε and θ subunits with other subunits. Conclusion: The similarities and divergences among various GABA_A subunits may be an important cause of different distribution and function of GABA_A subunits in different region of the central nervous system.