In this study, acidic and metal complexation properties of five humic acid samples, obtained from different source, were investigated. Humic acid samples were extracted with 1 M NaOH solution and then precipitated using concentrated HCl. Thus, purified humic acid samples were used in neutralization and Cu(II) complexation experiments. Purity of the humic acid samples varies between 75-85 %. Structural analysis of purified humic acid samples were performed by using FTIR, SEM and LC-MS methods. Molecular weights of them were determined by the aid of LC-MS method. Distribution coefficients (K-D) of humic acid samples in convenient solvent were also investigated and calculated. The data gained as a result of potentiometric titration were evaluated in Irwing-Rossotti method. Thus, acidity constants of -COOH and -OH groups, that can release proton, and formation constants of Cu(II) - humate complexes were determined. All experiments were performed at 2 degrees C and 25 degrees C.