Display omitted •A water-based ferrofluid was irradiated with photons and electrons.•The dose was that usually involved in radiation therapy of human subjects (50 Gy).•Electron irradiation induced minor change in the colloidal stability of ferrofluid.•Magnetic heating of ferrofluid at 100 kHz is not affected by irradiation.•Magnetic hyperthermia can be applied in the same time period as radiation therapy. The paper reports on the effect of therapeutic-like irradiation of a water based magnetic fluid with magnetite particles double-surfacted with oleic acid on its magnetic heating characteristics. To assess the effect of irradiation, a quantity of the initial sample was retained as the reference sample. The other part of the ferrofluid was irradiated with a photon beam (with the energy of 10 MeV and the dose of 50 Gy) and with an electron beam (of the energy of 9 MeV and the dose of 50 Gy). The frequency dependence of the complex magnetic permeability, μ(ω) = μ′(ω)-i μ″(ω), was affected only in the case of the electron irradiated sample and over the approximate range of 10–100 kHz. The dynamic light scattering investigation revealed a small increase of the average of the size of light scattering entities and of the polydispersity index of the sample irradiated with electrons compared to the reference sample. Magnetic heating experiments, performed at the frequency of 100 kHz and with various amplitudes of magnetic field, H, (of 25, 50, 75 and 100 Oe) did not reveal significant difference in the heating rate values of the reference sample and of the irradiated samples. Therefore, magnetic hyperthermia can be involved in the therapy plan, in the same period of time as the radiation therapy, provided at the frequency of the alternating magnetic field larger than the frequency corresponding to the Brownian relaxation peak.