A method of producing a three-dimensional cell structure includes producing a mixture of a cell cluster including an endothelial cell, an extracellular matrix component, and a polymer electrolyte, removing a liquid from the mixture to obtain a cell aggregate, and culturing the cell aggregate in a medium to obtain a three-dimensional cell structure with a thickness greater than 150 μm and having a vascular network. The extracellular matrix component is collagen or a collagen analog, and the polymer electrolyte is heparin or a heparin analog having a final concentration of 0.001 mg/mL or higher in the mixture.