The behavior of the trivalent ion praseodymium in 2M of NaCl at 303 K and in CO2 free conditions, was studied. Spectrophotometric titrations of the soluble species were used, in order to obtain the value of the first hydrolysis constant of Pr(III). The data obtained were treated with both the program SQUAD and by a graphic method, respectively. The result obtained using SQUAD was log*ß1 = –8.94 ± 0.03, while it was log*ß1 = –8.77 ± 0.03, when calculated graphically. These results are similar to the value obtained previously with the potentiometric method.