Abstract The effect of gamma radiation on the color intensity of aerated and oxygenated aqueous solution of bromophenol blue (BPB) was investigated. Ionizing radiation at increasing absorbed doses ( D) brought about gradual bleaching (i.e. decrease in optical absorbance, -Δ A) of bromophenol blue solutions. The molar extinction coefficients of acidic, neutral, and alkaline solutions were measured and found to be independent of temperature during spectrophotometry between 20 and 40°C. Aerated and oxygen-saturated acidic solutions showed a linear response -Δ A vs D) up to doses of 2.4 and 2.1 kGy, respectively. Aerated alkaline solutions on the other hand showed a linear response up to 4.8 kGy. The decoloration yields for 5 × 10 -5 M bromophenol blue aqueous solutions, G(-BPB), obtained from the decrease in absorbance at 591 nm wavelength for acidic, neutral, and alkaline solutions, were 0.244, 0.113, and 0.098 (100 eV) -1, respectively. The first-order rate constant for the reaction of OH radical with bromophenol, obtained from competition reactions with ethanol at pH 4, was found to be 9.1 +- 1.2 × 10 9 M -1 s -1. The degree of decoloration of bromophenol blue in acidic solutions was found to decrease upon the addition of ethanol, G(-BPB) decreasing from 0.24 to 0.088 upon the addition of ethanol at a concentration of 10 -2M. Suggestions are made for possible radiation dosimetry in the dose range (0.1–5 kGy) by means of spectrophotometric analysis of absorption spectra.