[en] The development of the delayed fission neutron counting method for uranium and thorium analysis in many kind of sam pas such as monazite mineral, uranium - thorium cake and both organic and inorganic solutions were studied. The interference of thorium to the determination of uranium included the sensitivity, precision and accuracy were evaluated. The suitable quantity of the samples and the comparison between the delayed fission neutron counting method and the neutron activation method for uranium and thorium determination were also reported