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A detailed study of Zn(II)-D-mannosamine and mixed ligand complex Zn(II)-D-mannosamine-glycine in aqueous solution ( θ = 25 °C, I c = 0.55 mol L −1 ) was carried out by voltammetry and potentiometry, allowing their characterization. Redox process of the [ZnManN] 2+ complex was registered at E p ∼ −1.01 V, [ZnGly] + at −1.02 V, ZnGly 2 at −1.18 V, while [ZnManNGly] + at −1.12 V (pH = 8.0). Stoichiometry and stability constants of Zn (II) complexes were determined by potentiometric titrations. Calculated stability constants were found to be: log   β ZnManN 2 + = 2.7, log   β MaNZnGly + = 7.7 and log   β MaNZnGlyH − 1 = −0.15. Voltammetric and potentiometric data were in good agreement, both indicating formation of two different ternary complexes, i.e. [ZnGlyManN] + and [ZnGlyManNH −1 ]. Calculated speciation revealed the presence of the [ZnManN] 2+ complex, as well as ternary complexes ([ZnManNGly] + ) in significant amount. This study was the first attempt to quantify complexation processes of Zn (II) with naturally occurring amino sugar and mixed complex with amino acid, important for bioavailability of zinc (II) in seawater. [ABSTRACT FROM AUTHOR]