In this study the spectrophotometric response of the Toluidine Blue O (TBO)-gelatin gel dosimeter irradiated with gamma rays was characterized. Preparation of dyed-gelatin gel takes place in neutral medium; to give eventually gel dosimeter has a sharp absorbance peak at 635 nm that bleaches quantitatively upon irradiation and the colour change can be measured with UV-VIS spectrophotometer. The useful dose range was 1 - 150 Gy. The radiation chemical yield (G-value) of gel dosimeter was calculated and found to increase by increasing concentration of dye. Post-irradiation storage on the response of gel is discussed. The dose response function, radiation sensitivity, and dependences of the response on environmental factors were studied.