Provided is a method for forming a cell aggregate for self organization whereby it is possible to discover conditions necessary for fabricating a cell aggregate from numerous cells (tens of thousands to hundreds of thousands) in vitro and to realize complex higher order structures of a liver kidney or the like or interactions thereof with other organs. A method for fabricating a cell aggregate in vitro the method including culturing a mixture of at least a total cell count of 400 000 cells of any cell and/or tissue type and 100 000 to 400 000 mesenchymal cells and forming a cell aggregate having a size of at least 1 mm. A cell aggregate fabricated by the aforementioned method. A method for fabricating a three dimensional tissue structure the method including causing a cell aggregate fabricated by the aforementioned method to self organize and forming a three dimensional tissue structure endowed with a higher order structure. A gelled culture support the cross section of which on the culturing side thereof being U shaped or V shaped.
