Cryopreserved stem cells with high cell viability after thawing were obtained by slow freezing using a DMSO-free cryopreservation medium. Stem cells and/or progenitor cells thereof are contacted with a DMSO-free cryopreservation medium, comprising between 4 v/v % and 25 v/v % of propylene glycol and between 1.0 w % and 10 w % of a sugar; and are subsequently subject to a slow-freezing process. Optionally, the cryopreservation medium may comprise serum albumin and/or hyaluronic acid.