The acidity determinations method of humic acids (HA) content was developed by Schnitzer and Gupta and is a very well known procedure. Nevertheless, care is necessary to prevent measure errors due to non-controlled BaCO3 production, during the filtration and titration of HA total acidity. To overcome this problem, we developed in our laboratory a simple filtration and titration system for the determination of HA acidity under inert atmosphere. This system enables a better reproducibility and accuracy of total, carboxylic and phenolic acidity measures than those by Schnitzer and Gupta method.