The present study describes the coordination properties of a reduced Schiff base, N-(2-hydroxybenzyl)phenylalanine, towards cobalt(II) using potentiometric method. The speciation model was confirmed by UV–Vis studies. The appearance of a precipitate in the pH range 2-7.3 meant that measurements in aqueous solution were only possible in an alkaline medium. The results show the formation of four mononuclear complexes in aqueous solution with the different degree of ligand deprotonation. At physiological pH, the antimicrobial properties of N-(2-hydroxybenzyl)phenylalanine and of the Co(II)–ligand complexes were determined against Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Helicobacter pylori), Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis), and a fungal strain (Candida). The results indicated that both the complexes and the ligand alone exhibited anti-cellular toxicity against L929 mouse fibroblasts and gastric cancer cells. This double activity of the tested preparations prompts further study on the development of a composition to combat H. pylori infection and eliminate gastric epithelial cells with altered phenotype.