The present invention relates to a novel injectable delivery system for stem cell therapy, which comprises a thermo-sensitive amphiphlic chitosan nanogel. Therefore, the invention provides a method for repairing a tissue damage of a subject using the amphiphlic chitosan nanogel served as a carrier for delivering the stem cells to the damaged tissue. This invention also provides a method for sustaining the growth of stem cells using the amphiphlic chitosan nanogel served as a niche or scaffold.