The purpose of this study is to confirm the possibility of regenerating actual fat tissue using human adipose tissue-derived stem cells (ASCs) and hyaluronic acid-collagen sponge in animal model. Human ASCs of young female adults were isolated and culture expanded in basal media. At the second passage, cultured ASCs suspension containing 106 cells was applied on prewetted scaffolds the hyaluronic acid-collagen sponge and the sponges was exposed to adipogenic media for the 1week. Then the tissue engineered constructs were implanted into the subcutaneous pocket on the back of immunodeficient athymic nude mice for 3 weeks. Hyaluronic acid-collagen sponges without human ASCs were used as the control. After 3 weeks, specimens were harvested and adipogenic potentials were assessed with histological examination, RT-PCR for PPAR-γ2 expression and G-3-PDH activity. Tissue engineered fat tissue from ASCs and hyaluronic acid-collagen sponges demonstrated PPAR-γ2 positive expression and positive Oil red O staining. The histologic study showed definitive adipose tissue and rich vascular tissue within the engineered fat. Two-fold higher activities of G-3-PDH were identified in experimental group after 3 weeks as compared to control. By contrast, the specimen from control group did not show active vessel ingrowth and contained only few cellular elements within the scaffold. The control specimens failed to demonstrate adipogenic gene markers and were negative in oil red O staining. In conclusion, human ASCs can be differentiated into adipocytes and actual fat tissue engineering was possible with combination of adequate scaffold materials, such as hyaluronic acid-collagen sponges. These data demonstrate that fat tissue engineered from human ASCs can retain predefined shape and dimension for soft tissue augmentation and reconstruction of defects.