We have carried out systematic studies on the response of ferrous sulphate-benzoic acid-xylenol orange (FBX)—a highly sensitive chemical dosimeter in liquid form to accelerated charged particles of different LET. Dosimeters were exposed in the form of thin layers to graded fluence of ⁷Li ion beam with three different energies Viz, 46, 38 and 27 MeV corresponding to avera ge LETs of 6.3, 7.5 and 11 eV (Å^-1 and ¹²C ion beam with energy 45.6 MeV corresponding to average LET of 52.5 eV (Å^-1. From the investigations, the corresponding G(Fe⁺³) values were found to be (51.7 ± 1.3) x 10^-7, (35.4 ± 0.7) x 10^-7, (19.3 ± 0.6) x 10^-7 and (8.4 ± 0.1) x 10^-7 mol J^-1, respectively. For gamma radiation, with estimated LET of 0.02 eV (Å^-1,      G(Fe⁺³) value was observed to be (56.1 ± 0.4) x 10^-7 mol J^-1. Clearly, G(Fe⁺³) values were found to decrease with increasing LET of the particle beam. However, the dosimeter showed no dependence on LET up to about 6 eV (Å^-1 unlike the Fricke dosimeter. The results confirm the response of FBX dosimeter is non-linear for doses exceeding 5 Gy for ⁶⁰Co gamma rays. More importantly, the present study using ⁷Li and ¹²C ions clearly shows that response of the FBX dosimeter is linear for high LET radiations at low as well as high doses.