The binary and ternary systems of cobalt(II) and nickel (II) with the amino acids glycine, serine, aspartic acid and guanidinoacetic acid were studied. The amino acids glycine - Gly, serine - Ser, aspartic acid - Asp and guanidinoacetic acid - Gaa are all involved in several biochemical processes. These amino acids are constituents of many proteins, which are in turn, good complexing agents. The study of metal-amino acid interactions are of great interest, as they represent simplified models for the analysis of the changes caused in the proteins` properties, when these bond to metal ions. It was determined, in this work, the formation and interaction constants of species belonging to the binary and ternary systems of cobalt(II) and nickel(II). UV-Vis spectrophotometric analysis were also made for each of the systems studied. The comparison of the UV-Vis spectra in different pHs with the species` distribution graphs indicated a relationship between the d-d bands and the respective proposed specie. When analyzing the formation constants of the ternary complexes ML1L2, the Ni (II) complexes showed higher values than those of respective Co(II) complexes, a pattern which is in accordance with the Irving-Williams series. In conclusion to the comparison of the UV-Vis spectra with those in literature, we have that the bands found, as well as their respective position and molar absortivities, refer themselves to nonregular octahedral complexes. It was verified that the greatest intramolecular interactions beetween the ligands in the complexes studied were those of the species cointaining Gaa. From the graphs of species distribution in terms of pH, we were able to verify that in biological pH, for all three systems of Co(II), protonated ternary species were predominant. No generalizations were visible for the Ni(II) systems. In the Ni-Gly-Ser system, the specie NiGlySer is present in greater amounts in pH close to 7; in the Ni-Asp-Gly system, the ternary species are formed in lower quantities in lower pH values and in higher and biological pH values, binary species of hydrolyzed NiAsp are predominant; in Ni-Ser-Gaa systems, protonated ternary species are in higher concentration. In pH ~ 9, hydrolyzed (binary and/or ternary) species were found in all ternary systems. In more basic medium, the ternary species were fragmented, therefore generating ML(OH)3 and ML(OH)4 hydrolyzed binary species, which have in turn greater stability.