A new method for the preparation of 237 Np/ 238 U laboratory standards for accelerator mass spectrometry (AMS) measurement was developed at China Institute of Atomic Energy (CIAE). 237 Np was generated by β-decay (6.75days) of 237 U produced via fast neutron induced 238 U(n,2n) 237 U reaction. The 58 Co(n,2n) 59 Co and 93 Nb(n,2n) 92m Nb reactions were used to monitor the integral incident neutron flux. The cross-section of 238 U(n,2n) 237 U was determined by measuring the emission rate of 208.0keV γ-rays from 237 U decay with a calibrated HPGe γ-ray spectrometer at CIAE. In order to correct for the self-attenuation of 208.0keV γ-ray in the U sample, a 177 Lu–U method was introduced. The new correction method provided effective and high quality measurements of the cross-section for the 238 U(n,2n) 237 U reaction; and the 237 Np/ 238 U ratio. A series of AMS standards for 237 Np/ 238 U (10 −9 –10 −13 ) can be obtained by successive dilution of the original standard sample.