237Np (≃2.14 × 106 yr half-life) is potentially applicable in studies on nuclear safeguards and radioactive waste migration. The atomic ratio of 237Np/U in nature is 10−12 or even lower, depending strongly on the integral neutron flux received by the material. As an ultra-sensitive technique, accelerator mass spectrometry (AMS) is the best for measuring ultratrace 237Np. By extracting negative molecular ions NpO– from the oxide sample using 238UO– and 208Pb16O2
– pilot beams for the simulation of 237Np ion transport, identifying the interference isotopes by high-resolution dedicated injector, electrostatic analyzer, and time of flight (TOF) detector, a method for AMS measurement of 237Np was set up on the HI-13 accelerator at the China Institute of Atomic Energy (CIAE). A sensitivity of <10–11 has been achieved for the isotopic ratio 237Np/238U.