The present neutron-scattering experimental findings concern with a study of fragility of trehalose, maltose, and sucrose/water mixtures. The fragility degree has been characterized by a new definition based on the correlation between viscosity and mean-square displacement as obtained by elastic incoherent neutron scattering. The fragility values obtained for the homologous disaccharides/water mixtures are compared with those obtained for other glass-forming systems of different "strength". The less-fragile character of the trehalose/H2O mixture in respect to maltose and sucrose/H2O mixtures is finally linked to the better bioprotective capability.