This study investigated an effective method to desorb CO2 from low-concentration (0.2 mol/L) monoethanolamine (MEA) solutions using calcium chloride (CaCl2) and ultrasound irradiation at 25 ºC. The pH value of the solution had a large influence on the desorption ratio of CO2 from MEA solution under ultrasound irradiation. CO2 was successfully desorbed up to pH8.2, and it was impossible to desorb CO2 at pH over 8.2. It was clarified that CO2 desorption by ultrasound irradiation is useful for the concentration of MEA solution of up to 2.0 mol/L, because the pH rises above 8.2 when the concentration of MEA solution is increased to above 2.0 mol/L. It also became evident that the addition of small amount of CaCl2 further increases the amount of CO2 desorbed during ultrasound irradiation.