Process for producing ganglioside G.sub.M1

A process for preparing ganglioside G.sub.Ml selectively which comprises subjecting a solution of ganglioside or a mixture of gangliosides to the action of neuraminidase isozyme S obtained from a culture of a bacterium of Arthrobacter ureafaciens M1057, wherein the ganglioside or the mixture of gangliosides is at least one member selected from gangliosides G.sub.Dla, G.sub.Dlb, G.sub.Tla, G.sub.Tlb and G.sub.Qlb or a mixture of gangliosides extracted from bovine brain.