The present invention relates to a stable and readily usable administration type including a composition including mesenchymal stem cells cultured in hydrogel, more specifically, a adipose tissue-derived mesenchymal stem cell-hydrogel composition and a method of preparing the same. More specifically, the present invention relates to a composition including mesenchymal stem cells cultured in hydrogel, washed, and filled into a syringe, wherein the composition of the present invention may be readily administered without modification and may not need an enzyme treatment in a final process of preparing transplanted cells, almost no cell is lost because the composition is washed as hydrogel without an washing process using centrifugation or other methods, and the therapeutic effect is shown immediately after administration to an individual because bioactive substances are patched in pores of the hydrogel.