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Studies of using mesenchymal stem cells to assist skin and soft tissue expansion have shown that stem cells can improve expansion efficiency through promoting tissue regeneration. However, the issue that whether the flap viability is also improved is unknown.Sixteen pigs were equally divided into 2 groups. A pair of 150 mL expanders was symmetrically inserted into each pig's dorsum. Group 1 received adipose-derived stem cells (ADSCs) injection before expansion, and group 2 received ADSCs grafting after flap elevation. After 4 weeks' expansion, a random flap measuring 2 cm × 16 cm was elevated along the long axis of each expanded flap on the pigs' back. Flap viability was measured at postoperative day 7. Histological analysis and cell tracking were performed. The expression of vascular endothelial growth factor was determined.The flap viability of the ADSCs-grafted expanded flap (75.5 ± 6.6%) was similar to the control (69.4 ± 8.4%) in group 1 (transplantation before expansion). However, in group 2 (transplantation after flap elevation), the ADSCs-grafted expanded flap had a higher flap viability (92.6 ± 5.7%) compared with control (66.2 ± 7.4%). Moreover, the ADSCs-grafted expanded flap in group 1 showed increased skin thickness, collagen content, cells proliferation, vascularization, and vascular endothelial growth factor expression. Cell tracking showed that the positively stained cell differentiating into an endotheliocyte could be seen in group 2.Transplantation of ADSCs before tissue expansion does not improve flap viability but can promote tissue regeneration. Injection of ADSCs after flap elevation can increase the surviving rate of the expanded flap.