CO2 solubility in the solutions of three types of tertiary diamines, N,N,N',-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,3-diaminopropane, and N,N,N'-,N'-tetramethyl-1,6-diaminohexane, was measured using vapor-liquid equilibrium., equipment at temperatures from (313 to 393) K and pressures from (10 to 500) kPa. For these tertiary dial-nines, the CO2 solubility was calculated based on a simplified chemical equilibrium model. It was bserved that alkyl chain length between two amines has an important tole in CO2 solubility. To clarify this role, we also performed quantum Mechanical calculations using the density functional theory and a continuum solvation niodel