Equilibrium study on the mixed ligand complex formation of Cu II with biguanide(Bg) and glycine (HG), indicated the formation of the complexes: Cu(Bg) 2+, Cu(Bg) 2 2+, Cu(Bg-H)(Bg) +, Cu(Bg-H) 2, Cu(Bg)(OH) +, Cu(Bg-H)(OH); Cu(G) +, Cu(G)(OH), Cu(G) 2; Cu(G)(Bg) +, Cu(G)(Bg-H); (G)Cu(Bg)Cu(G) 2+, (G)Cu(Bg-H)Cu(G) +, and (G)Cu(Bg-2H)Cu(G). From the deprotonation constants of coordinated biguanide (Bg) in the complexes Cu(Bg)(OH) +, Cu(Bg-H)(Bg) + and Cu(G)(Bg) +, the Lewis basicities of the coordinated ligand species (Bg-H) -, OH - and glycinate (G -) were found to be of the order: (Bg-H) -≫ OH -> G -. Bridging (N 1-N 4, N 2-N 5) tetradentate mode of coordination by biguanide species Bg, (Bg-H) - and (Bg2H) 2- was indicated from the occurrence of biguanide-bridged dinuclear mixed ligand complexes (G)Cu(Bg)Cu(G) 2+, (G)Cu(Bg-H)Cu(G) +, (G)Cu(Bg-2H)Cu(G) in the complexation equilibria. © Indian Academy of Sciences.