The present invention provides: a mammalian stem cell suspension containing mammalian stem cells and a polysaccharide such as trehalose； a mammalian stem cell aggregation inhibitor containing a polysaccharide such as trehalose； a method for inhibiting the aggregation of mammalian stem cells whereby mammalian stem cells are suspended in a physiological aqueous solution containing a polysaccharide； an inhibitor for reducing the survival rate of mammalian stem cells containing a polysaccharide such as trehalose； a method for inhibiting a reduction in the survival rate of mammalian stem cells whereby mammalian stem cells are suspended in a physiological aqueous solution containing a polysaccharide； and the like.
