In generic neutronic studies of a fusion breeder, resonance absorption is mostly neglected. In this work, the effects of resonances on the neutronic parameters a fast and moderated fusion blanket are investigated. In the present case, a (D,T) fusion reactor acts as an external high energetic (14.1 MeV) neutron source. The fissile fuel zone, containing 10 rows in radial direction, covers the cylindrical fusion plasma chamber. The fissile fuel is natural UO2. Fissile zone is cooled (a) with pressurised helium gas for the fast blanket and (b) with light water for the moderated, each of them with a volume ratio of V-coolant/V-fuel=2 in the fissile zone. The study has shown that careful resonance self-shielding calculations are indispensable for neutronic studies of a moderated fusion blanket. On the other hand the omission of the resonance self-shielding in generic studies of a fast fusion blanket can be tolerated to some degree. Furthermore, a correct description of the fusion neutron source spectrum has great importance on neutronic parameters, along with the resonance self-shielding calculations. (C) 2002 Published by Elsevier Science Ltd.