In this study, it is aimed to investigate neutron self-shielding effect in application of k(0)-NAA standardization method to determine Mn contents in manganese ores. Because the neutron self-shielding correction factors are significant factors in application of k(0)-NAA method for large samples. To estimate these, several Mn-ore samples and Au monitor were irradiated separately in a 37 GBq Am-241-Be neutron source irradiation unit and then they were measured by using a 78.5% relative efficient HPGe detector. In this study, the sigmoid function approaches for calculation of G(th) and G(e) factors were applied for the right cylinder sample geometry at known elemental compositions in samples, determined by EDXRF technique with a 25 mm(2) Silicon Drift Detector (SDD). The present results indicate that k(0)-NAA method is applicable successfully to determine Mn contents in Mn-ore samples providing that G(th) and G(e) factors are estimated accurately even if a low-flux isotopic neutron source is used.