To study the effect of the conformation of sugar hydroxy groups on metal complexation processes, complex formation of eight saccharides (D-fructose, L-sorbose, L-arabinose, D-arabinose, D-glucose, D-sorbitol, 2-deoxy-D-glucose and D-saccharose) with dimethyltin(IV) cations was investigated in aqueous solution by potentiometric equilibrium measurements, 1 3 C NMR, polarimetric and Mossbauer spectroscopic methods. The experimental results proved that deprotonation of D-fructose and L-sorbose is caused by the coordination of dimethyltin(IV) in the unusual low pH interval 4-6 in contrast to the other saccharides deprotonated in analogous way at pH>8. Increasing the pH of the solution resulted in the formation of further complexes. Stability and composition of the species was determined by potentiometric studies. 1 3 C NMR measurements led to the assignment of the sugar OH groups participating in the processes. Mossbauer investigations in the quick-frozen solutions permitted the determination of the stereochemistry of tin(IV) in the complexes.