Extensive ferromagnetic resonance (FMR) measurements have been performed in the critical region, -0.15 ≤ ϵ =( T− T C )/ T C ≤0.15, on amorphous Fe 78W 5B 17 and Fe 74W 9B 17 alloys, before and after they had undergone isothermal annealing treatment at a temperature T A = 400 K for durations of time t A = 1 and 2 h. The values of saturation magnetisation, M s, and resonance field, H res, at different temperatures are accurately determined through an elaborate lineshape analysis of the observed FMR spectra. From the M s( H res, T) data so obtained, the asymptotic values of the critical exponents β and γ for spontaneous magnetisation and initial susceptibility are estimated using the ‘range-of-fit’ scaling-equation-of-state analysis. Consistent with the predictions of the infinite three-dimensional (3D) ferromagnetic (FM) matrix plus finite spin clusters model and with the well-known Harris criterion, isothermal annealing, which enhances the value of the Curie temperature, T C, considerably, leaves the values of the exponents unaltered from their ‘as-quenched’ values, which are close to those predicted by 3D nearest-neighbour Heisenberg model. In the critical region, the Gilbert damping parameter and the Landé splitting factor are temperature-independent and structural relaxation has no effect on them.