Provided is an adhesive composition disclosed herein includes tannin, poly(ethylene glycol) and water. The adhesive composition has little toxicity, allows adhesion even in the absence of a thermosetting curing agent, and is hardly soluble in water to show moisture resistance, unlike known tannin adhesives. Therefore, the adhesive composition may be used as a medical adhesive, adhesive depot for sustained release of drug, anti-adhesion agent, cell/protein adsorption barrier and medical hemostatic applicable to various wet environments.