A substratum for cell culture which comprises a chemically modified collagen rich in either positive or negative charges when under culture conditions. The substratum is prepared by modifying the amino groups or carboxyl groups of collagen. The chemically modified collagen enhances the adherence and proliferation of animal cells much more actively than unmodified collagen in the presence or absence of bovine fetus serum. The cultured animal cells can be detached efficiently from the chemically modified collagen. This allows for highly selective isolation and recovery of the cultured animal cells which can be accomplished without incurring any injury from the chemically modified collagen.