The low cycle fatigue property of the Zr-4 cladding before and after the neutron irradiation is investigated in this paper. The stress-strain curve and the Coffin-Manson relation of the pre-irradiation specimens are first obtained. Then an estimation of the effect of the neutron irradiation on the low cycle fatigue property of Zr-4 cladding is obtained. The fatigue crack microstructure is analyzed and the mechanism of the fatigue is discussed. It is shown that the Zr-4 tube sees a serious irradiation-embrittlement. Both non-irradiated and irradiated specimens show cyclic softening. The strength coefficient and the hardening exponential are increased, the material constant is decreased and the life of the Zr-4 tube is reduced after the iradiation.