Fire retarding and smoke inhibiting aqueous composition and a method for a one-step impregnation of aqueous-absorbable--and normally inflammable materials, such as wood, paper and textiles, said composition comprising ammoniumphosphates, phosphoric acid, water soluble metal salts with ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions, and other optional additives.The composition comprises in combination:0.5-90% by weight monoammoniumphosphate and/or diammoniumphosphate,0.1-30% water-soluble metal salts with ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions,1-20% by weight acid especially phosphoric acid (85%),1-15 % by weight dicyandiamide, andoptionally up to 5% by weight additivesin a total concentration of from 1 to 50% by weight with respect to the total weight of the aqueous solution, whereby phosphoric acid and dicyandiamide are present in the form of the reaction product guanylureaphosphate.