A cell preparation containing mesenchymal stem cells whose immunosuppression ability is maintained is produced by means of a serum-free or low-serum culture. A method for producing a cell preparation containing mesenchymal stem cells, comprising the steps of: (A) proliferating mesenchymal stem cells in a serum-free medium “A” containing an FGF, a PDGF, a TGF-β, an HGF, an EGF, at least one phospholipid, and at least one fatty acid; and (B) screening mesenchymal stem cells whose immunosuppression ability is maintained or improved, from the mesenchymal stem cells thus proliferated in the step (A).