Changes of exchangeable acidity in the soil colloid of a latosol and a red soil with the presence of NaCl and Ba(NO₃)₂ solutions were studied quantitatively with an automatic pH control titration device.The results showed that in the two salt solutions only exchangeable acidity appeared in the range of pH measured.The amount of exchangeable acidity in the red soil is larger than that in the latosol.The increment of exchangeable acidity decreased with increase in concentration of the salt solutions.Turning points in the curve of the exchangeable acidity were observed when 300 mmol kg^-1 of NaCl and 120 mmol kg^-1 of Ba(NO₃)₂ was added respectively.The exchangeable acidity, which were significantly influenced by pH,increased with pH in the Ba(NO₃)₂ solution,but the peak value of the exchangeable acidity was found in the NaCl solution. A method of measuring the Cl^- exchangeable alkalinity was constructed.