A method is disclosed for cryopreserving living animal cells in immunoisolation membranes, including: (1) cutting out a living organ from an animal, (2) digesting the cutout organ into the discrete living animal cells and separating the discrete cells, (3) suspending the separated cells in a solution of sodium chloride containing sodium alginate and collagen, (4) forming microcapsules of the living animal cells by using the resulting suspension, (5) forming immunoisolation membranes around outer surfaces of the microcapsules of the living animal cells by covering the outer surfaces with alginate-(poly-L-lysine) and thereby obtaining the living animal cells enclosed in the immunoisolation membranes, (6) suspending the resulting living animal cells enclosed in the immunocapsules in a cell damage-preventing solution, and (7) immediately freezing the thus obtained suspension with liquid nitrogen.