The physical properties of the absorbent are important for designing a CO2 capture process. The density and viscosity are used to calculate the mass transfer coefficient that determines the height of the absorber. Furthermore, these physical data affect the selection of liquid pump and pipe lines. Vapor pressure is a factor that estimates absorbent loss and condenser size. In this study, the physical properties of the aqueous potassium carbonate (K2CO3)+2-methylpiperazine (2MPZ) solution were obtained in a temperature range from 303.15 K to 343.15 K. The physical properties of the different aqueous K2CO3+2MPZ solutions (various amine concentrations and amounts of CO2 absorbed) were measured to obtain the parameters for process design. A regression analysis was conducted for the experimental data. The densities of the aqueous K2CO3+2MPZ solutions increased when the amounts of absorbed CO2 or 2MPZ concentrations were increased. The densities and viscosities of the absorbents decreased according to the increase in temperature. The viscosities of the absorbent increased when 2MPZ concentrations were increased. The temperature dependency of vapor pressure follows the Antoine equation; the CO2 gas and aqueous solution of a base follows the vapor pressure variation of the mixed solution.