To impart biodegradability to a water-absorptive resin to cause natural anabolism and to obtain a fire extinguishant compsn. friendly to the natural environment by preparing the compsn. consisting of the water-absorptive resin having the biodegradability, a fire extinguishing chemical, a thixotropic agent and water.

The water-absorptive resin having the biodegradability to be used refers to a crosslinked polyaspartic acid based resin. This resin is a polymer compsn. consisting of at least ≥50 wt.% aspartic acid or succinimide (or aspartic anhydride) as a component. The fire extinguishing chemical of a nitrogen compd. or phosphoric acid compd. is dissolved into the water to be absorbed in order to improve a fire extinguishing effect. The thixotropic agent is added to the fire extinguishant, by which the fire extinguishant is made low in viscosity at the time of fire extinguishing action. The fire extinguishant exhibits a sufficient flow property and hardly flows down after the adhesion to the object to be fire extinguished and, therefore, an effect of sustaining fire extinguishment in a vertical face is enhanced.