ESR studies of irradiated lyoluminescence (LL) phosphor, trehalose dihydrate showed a linear free radical growth upto a dose of 11 kGy. The LL output measured under oxygen equilibrated conditions showed an extension of the dosimetric response from 0.6 to 6k Gy. ESR spectral analysis indicates the formation of two radical species viz., ‘a’ and‘b’ and their involvement in the LL process. The estimated free radical concentrations of radicals ‘a’ and ‘b’ were found to be 6.81x1015 and 1.35 x 1016 g-1, respectively, for a gamma dose of 10.8k Gy.