Resumo. The objective of this work was to evaluate the efficiency of fire retardant in relation to the applied volume and the application period. The experiment has been realized on the Forest Fire and Nature Conservation Laboratory of the Federal University of Viçosa (UFV), in Minas Gerais, Brazil. After the solution application of 600 and 900ml/m² on five repetitions, the efficiency has been evaluated during four weeks. Parcels of 3,0 X 1,0 m have been built in a ramp with mean inclination of 27º. It has been spread 1,20kg/m² of Melinis minutiflora Beauv as burning fuel on the area. The product efficiency has been evaluated comparing the applied quantities and the application period observing the flames height, cover speed, burn intensity and burn period on the portions with and without the product. The relative air moisture and the fuel material moisture at the burn moment have been determined. The results have shown that the application period did not have influence on the product action. The mean period that the fire line took to cover the parcel with the product was, in average, seven times slower than the part without the product. The burn intensity was around eight times minor, despite the fire covered all area. The same occurred to the flames height which was three times lower than the area without the product.