The decoloration behavior of an aqueous solution of Reactive Red 120 (RR-120) dye was investigated spectrophotometrically at different doses and at different solution compositions. The dye dosimeter was formulated by comparing the sensitivity of RR-120 decoloration relative to the dose in an independent hydrated electron (eaq-) and hydroxyl radical (•OH) dominating reactions. An aqueous solution of 1.0x10-3 mol dm-3 RR-120 containing 1.5 mol dm-3 tert-butanol in a N2 purged system can be employed to determine doses in the range of 0–6.0 kGy with a sensitivity of -0.143kGy-1 and coefficient of determination (R2) of 0.999. The sensitivity of the dosimeter increased, but the linear dynamic range decreased, with a decrease in the initial dye concentration. There activity of (eaq-) with RR- 120 increased upon increasing the initial dye concentration, while the reactivity of eaq- with intermediate reaction products decreased under the same condition. The preferred reactivity of eaq- with RR-120 increased the linear dynamic range of the dye dosimeter with little compromise in its analytical sensitivity. The N2 purged aqueous solution of 1.0x10-4 mol dm-3 RR-120 containing 0.15 mol dm-3 tert-butanol was found to be the most suitable condition to measure doses in the range of 0–0.25 kGy with a sensitivity of _1.679kGy-1 and R2 of 0.999.The N2 purged aqueous solution of 5.0x10-5 mol dm-3 RR-120 containing 0.1moldm-3 tert-butanol was found to be the most suitable condition to determine doses in the range of 0–0.15kGy with a sensitivity and R2 of -3.903 kGy-1 and 0.999, respectively. We developed three types of dye dosimeters for different linear dynamic ranges with specific sensitivities, precisions and accuracies. The choice of the dye dosimeter depends on the demand in the linear dynamic range, sensitivity, precision and accuracy, and thus, the dye dosimeters are highly task specific. The present work reports the preliminary experiments on the feasibility of developing a reproducible and task-specific dye dosimeter for accurate measurement of gamma radiation doses and that is useful indifferent applications.