Logarithms of stability constants, log β, of copper(II) complexes with tripeptides containing glycine, glutamic acid, and histidine were modelled with 3χv connectivity index. The model developed on complexes with tripeptides formed of Gly and Glu yielded S.E. = 0.47, 0.38, and 0.55, depending on whether CuL, CuH−1L, or CuH−2L complexes were taken as referent. The model was also applied to complexes with tripeptides containing His, S.E. = 1.47, 1.39, and 1.80. Although a somewhat worse result for G/E/H tripeptide complexes, much bigger range of their log β’s (29.648), in contrast to 16.671 for G/E tripeptide complexes, has to be borne in mind.