In this study, we examined the complex formation of the Cr(III) ion with a variety of biological pH buffers [tris(hydroxymethyl)aminomethane (TRIS), N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES), N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS), N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO), N-tris(hydroxymethy)methyl-4-aminobutane sulfonic acid (TABS), 4-morpholine ethane sulfonic acid (MES), 4-morpholine propane sulfonic acid (MOPS), 3-morpholino-2-hydroxypropane sulfonic acid (MOPSO), and 4-(N-morpholino)butanesulfonic acid (MOBS)] by potentiometric measurements at 310.15 K and ionic strength I = 0.16 mol . dm(-3) KCl. The protonation constants of the biological buffers were determined and discussed, under the above conditions. The overall stability constants were obtained by the least-squares curve-fitting program HYPERQUAD 2008. As a result of the numerical treatment, a model composed of five main species CrL, CrL(2), CrL(2)(OH), CrL(2)(OH)(2), and CrL(3) was obtained, where L = TRIS, TAPS, TAPSO, TABS, and MOBS. The first four complexes have also found from the systems containing MES, MOPS, or MOPSO. The stabilities of the binary complexes appear to follow the order TABS > TAPSO > TRIS > TAPS > TES and MOBS > MOPS > MOPSO > MES for the TRIS family and morpholine family, respectively. The trend in stability constants of the binary complexes was discussed. The species distribution diagrams of Cr-(buffer)(x)-(OH)(y) systems were evaluated as a function of pH. In addition, the influence of CH(2) (between the zwitterions) and OH (nearby the sulfonic group) on the stability constants was studied. The results show that the insertion of methylene groups between the amino group and the sulfonic group enhanced the complexation. While the (OH) group of TAPSO may be taking part in coordination with the Cr(III) ion, it is not for MOPSO.