Abstract: In this paper, a particular RNAA procedure is designed to quantitatively determine trace 236Np in the complex samples containing Ca, Al, Mg, Fe, Th, U, 237Np, Pu, Am, Cm and fission products. The samples are separated and purified by anion exchanger and PMBP levextrel resin and irradiated in a reactor (flux. 3.2×1 014n/cm2·s) , 237Np is adopted as the interior standard. Then ratio of nucleus R236PU/238pu in the activation products of the samples are determined by a α-spectrometer. The measurements results show that the contents of 235Np are (1.29±0.23)×10-14g/g.