The advantages of using optical fibres as ionizing radiation sensors are discussed. The radiation induced transmission loss of a plastic clad silica (PCS) optical fibre has been investigated with respect to suitability for dosimetry purposes at 6 0 Co source irradiation applications. It is found that the response of PCS fibre is strongly linear with dose up to 10 3 Gy and stable in time, with sensitivity 1.47 10 - 1 dB/km Gy at 0.6 μm wavelength of the conducted light.