Three-dimensional (3D) cell co-culture has received much attention in various applications including tissue engineering.Since hydrogels,such as an alginate gel,are biocompatible and flexible materials,they are used for 3D cell culture [1].Since alginate gels can be fabricated by simply reacting Ca2+,alginate gels have widely been applied to tissue engineering.Recently,a novel method on alginate gel electrodeposition was reported [2].In the method,electrolysis of water in alginate solutions with CaCO3 particles induced gel aggregation on the electrode surface (Fig.1).In this study,we proposed a novel method for 3D co-culture system using electrodeposited alginate gels,and tubular structures or microwells of alginate hydrogels were fabricated to prepare 3D cultured cells.Alginate gels were electrodeposited around the Pt wire electrode for fabricating tubular cell structure [3].The HUVECs (normal human umbilical vein endothelial cells) labeled with Cell Tracker Green or 3T3 cells (mouse fibroblasts) labeled with Cell Tracker Orange were suspended in 1% alginate sodium solution with 0.5% CaCO3 and the alginate gel including cells was sequentially fabricated around the Pt wire electrode by electrodeposition.After gelation,the Pt wire electrode was removed and the hollow alginate gels were cultured in the medium.The tubular gels consisting of double layer of HUVECs and 3T3 cells were successfully fabricated (Fig.2) Next,hydrogel microwell arrays were fabricated on the patterned ITO electrode and HepG2 (human hepatocellular carcinoma cells) were co-cultured with 3T3 cells in the hydrogel microwells (Fig.3).To investigate the functions of the HepG2 spheroids,liver-specific gene expressions of the HepG2 spheroids were evaluated by qRT-PCR.The expression levels were substantially increased by inducing the 3D co-culture,which indicates that we successfully fabricated in vitro liver model.These results show that these approaches are useful to fabricate 3D co-culture cells for tissue engineering.