We report ESR measurements in the spin-glass-like system Fe 1 − x Ga x SbO 4 for 0≤x≤0.8. A single broad line associated with the resonance of Fe 3 + is observed at g=2.00(5). The temperature dependence of the ESR linewidth shows two different regimes. Between 200 and 640 K the temperature dependence is discussed in terms of a mean-field approximation for the magnetic interactions between neighboring Fe ions, and the experimental data have been correlated to the behavior of the static magnetic susceptibility. From this analysis we have determined the high-temperature limit of the linewidth, Δ H p p (∞), for different values of x. Below approximately 200 K a strong enhancement of the linewidth is observed, and, from the temperature dependence measured in this region, we have estimated values of the spin-freezing temperature for different concentrations of magnetic ions and determined a concentration of Ga atoms, x 0 =0.285(15), above which there is no evidence of spin freezing for T>4.2 K. The large absolute value of the high-temperature linewidth for FeSbO 4 and its increase when the system is magnetically diluted through Ga substitution indicate the importance of spin-diffusion processes in these materials. This observation, together with the comparatively high magnetic-percolation concentration determined from the x dependence of the freezing temperature, suggest that large portions of the system may present low-dimensional magnetic behavior. This possibility is analyzed in terms of the antisite cationic order proposed for these compounds.