Alginate was a proven biocompatible biomatrice for cells but it was known not to provide a proper microenvironment needed for the proliferation of cells because of its anionic property, which caused its low affinity for cells. Water-soluble chitosan was well known as wound healing material and it also had cationic property which helped cell-to-matrix adhesion. The purpose of this study is to assess the ability of a chitosan/alginate mixed sponge as a scaffold for preadipocytes to serve as a biological implant for soft tissue augmentation. Chitosan/alginate and calcium alginate sponges were made by lyophilizing of alginate with water-soluble chitosan mixture and with calcium chloride mixture, respectively, and those were observed by SEM. Preadipocytes seeded in those sponges were cultured for 2 weeks. In vivo study was designed that chitosan/alginate sponges with and without preadipocytes were implanted subcutaneously into nude mouse. Chitosan/alginate and calcium alginate sponges which had highly porosity and 50-200㎛ pore size. In the chitosan/alginate sponge, the levels of DNA amount were significantly higher than those in calcium alginate sponge (P<0.05). In both groups, they increased progressively with time. On the in vivo study, it was observed that adipose tissue layer in the margin of chitosan/alginate sponge on the 2 weeks after implantation of nude mouse. On the 8 weeks after implantation, thick layer of adipose tissue and neovascularization were observed in the chitosan/alginate sponge. Consequently, chitosan/alginate sponge provided proper microenvironment to human preadipocyte, increased the cell proliferation and maintained the pore that offered neovascularization, so turned out to be effective form of fat transplantation for soft tissue augmentation and reconstruction.