Some natural aldohexoses reacted with [Ni(tn)₃]²⁺(tn = trimethylenediamine) to yield octahedral nickel(II) complexes containing glycosylamine ligands. The complexes were characterized by elemental analyses, magnetic moments, electronic and CD spectra. The molecular structure of [Ni(L-Rha-tn)₂]Br₂·2H₂O·MeOH [L-Rha-tn = 1-(3-aminopropylamino)-1,6-dideoxy-L-mannose]1 has been determined by single-crystal X-ray techniques: orthorhombic, space group P2₁2₁2₁, a= 12.373(1), b= 21.614(2), c= 11.272(1)Å, least-squares refinement led to a final R factor of 0.044 using 2657 reflections having F_o > 3σ(F_o). From X-ray crystallographic studies of glycosylamine complexes, two typical co-ordination structures of the aldose unit have been found in 1 and [Ni(D-GlcN-en)₂]²⁺[D-GlcN-en = 2-amino-1-(2-aminoethylamino)-1,2-dideoxy-D-glucose], which can be discriminated by the two geometrical isomeric forms arising from the two substituents on C¹ and C² of the pyranoside ring, namely cis and trans. The sugar unit of 1 has cis geometry containing equatorial and axial substituents on C¹ and C² of the pyranoside ring. In contrast, the sugar unit of the D-GlcN-en complex has trans geometry at these positions, which are both equatorial. Assuming the ⁴C₁(chair) conformers to be the most stable and based on some stereochemical considerations of both the sugars and the chelate rings, the structures of the sugar units in the glycosylamine complexes from all natural aldohexoses can be classified into either of the above two types, the only difference being the relative absolute configuration at C² and C⁵. This classification is well correlated with the CD spectral patterns obtained in methanolic solutions.