The aim of this study is to explain the interactions between two cell groups. The tissue consists of different types of cell groups. Interactions between cell groups are important for organ or tissue functionality. Using cell sheet technology, we have proposed models of tissue structure in vitro. These models are very useful for studying interactions between cell groups at gene expression level. We studied the interactions between rat hepatocytes and human endothelial cells (HEC). Functions of rat hepatocytes monolayer culture disappeared within ten days. On the other hand, rat hepatocytes and HEC bilayered cell sheet culture system maintained over forty-one days of differentiated cell shapes and functions. These results indicated the importance of interactions between hepatocyte and HEC cell groups. The layered co-culturing of hepatocytes and HEC sheets allows the former's continuous expression of differentiated functions, thereby offering a major advancement in surface modification of biomaterials.