Abstract: It is intended to provide a method of preparing a decellularized soft tissue whereby swelling after an ultrahigh pressure treatment can be inhibited, etc. The above-described method of preparing a decellularized soft tissue comprises the application step wherein an ultrahigh hydrostatic pressure is applied to an isolated soft tissue in a medium to thereby disrupt cells in the soft tissue, and the removal step wherein the disrupted cells are removed. As the medium, use is made of an aqueous solution containing a water-soluble polysaccharide such as dextran.