The present paper reports fire intensity reduction factors in partially retardant-treated straw fuel beds. Propagation experiments were carried out in the laboratory with fuel beds with a bulk density of 7.5 kgm_3 under no-slope/no-wind, up slope/no-wind and no-slope/wind-aided conditions. Fire-Trol 931, along-term retardant based on polyphosphates, was employed in these experiments and a single retardant concentration of 0.2kg of dry retardant product per kg of fuel was tested. It has been statistically inferred that fire intensity reduction factors are constant, regardless of the fire intensity of the flame front at the untreated area of the fuel bed, and a mean fire intensity reduction factor of 0.80 has been computed under the experimental conditions tested.