A method for providing a vascular system in biological tissue in vitro, the method comprising cocultivation of the biological tissue with vascular cells and mesenchymal cells. Biological tissue in which a vascular system has been provided by said method. A method for producing a tissue or organ, the method comprising transplantation of the biological tissue in a non-human animal and inducing differentiation to a tissue or organ in which a vascular network has been constructed. A tissue or organ regeneration or function-restoring method comprising transplantation of the biological tissue in a human or non-human animal and inducing differentiation to a tissue or organ in which a vascular network has been constructed. A method for producing a non-human chimera animal, the method comprising transplantation of the biological tissue to a non-human animal and inducing differentiation to a tissue or organ in which a vascular network has been constructed. A method for evaluating drugs using at least one selected from a group consisting of the biological tissue, tissues and organs produced by said method, and non-human chimera animals produced by said method. A regenerative therapy composition comprising biological tissue in which a vascular system has been provided by said method.
