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.