The invention provides a polyelectrolyte complex gel comprising a chitosan and a γ-polyglutamic acid (γ-PGA) having a molecular weight from about 1 kDa to about 400 kDa or the salt thereof, wherein the chitosan and the γ-PGA are swollen with an aqueous solution. Also provided is a soft tissue augmentation implant, comprising a polyelectrolyte complex gel of the invention as a carrier or a filler and an optional additive. The polyelectrolyte complex gel and the soft tissue augmentation implant containing the same has long degradation time and better supportability so as to provide good maintenance for soft tissue.