Several single mode silica-based fibers with different levels of erbium concentrations have been tested under 60Co gamma radiation. Irradiation has been performed at a dose-rate of ~30 Gy/h to a total dose of ~2 kGy. Transmission spectra were measured in situ in a spectral range from 1250 to 1630 nm. The measurements show no detectable change in the Er-ions luminescence and absorption spectrum profiles, while a significant (~dB/m/kGy at 1530 nm) increase in transmission losses is attributed to the silica host matrix modifications. This conclusion is drawn based on the post-irradiation photo-luminescence analyzes realized with a confocal micro-spectrometer (514.5 nm excitation, P ~2mW).