It has been widely known that Pd-Ni-Cu-P alloy system possesses the largest glass forming ability among the bulk metallic glasses. But its fragility exhibits relatively low index, lower than other good metallic glass formers. Intensive research has been done on glass forming ability, and it has been suggested that the sluggish diffusive motion and small driving force for nucleation are responsible for this unusual phenomena. However, this apparent contradiction between glass forming ability and fragility is not unique among vitreous materials. Considering the same details of vitrification of water and thermodynamic fragility, as well as unusual expansion during solidification of PdNiCuP metallic glass, it is suggested tentatively that there might be a fragile-to-strong transition during the vitrification of PdNiCuP metallic glass.