Polycrystalline ammonium dithionate has been examined for its radiation response in the low dose range (<5Gy) using EPR technique. The SO(3)(-) radical ion was detected as a single EPR line with a peak-to-peak derivative width of ca. 0.44mT in irradiated samples and its intensity was found to vary linearly with dose. At equal and moderate settings of microwave power and modulation amplitude ammonium dithionate was at least seven times more sensitive than l-alanine which is the most common EPR dosimeter standard. Pulse experiments were performed on the powder samples to obtain the longitudinal relaxation time. These and microwave saturation experiments served to indicate the optimal microwave power to be applied during measurements as an EPR dosimeter for best sensitivity of this material. It is thus claimed that ammonium dithionate has excellent potential to become an EPR dosimeter with a low limit of the measurable dose for cases where tissue equivalence is not required or can be corrected for.