The activation of gold by environmental neutrons through the reaction ¹⁹⁷Au (n,γ) ¹⁹⁸Au was used to study the effect of concrete buildings on the neutron flux, and to estimate the thermal neutron flux inside and outside these buildings. The results showed that three ceilings of thickness 34 g/cm² decrease the fast neutrons to 26% from its original value. However, the same reinforced concrete decreases the slow neturon flux to only 62% of its original value. The thermal neutron flux at 283 m from the center of training Reactor of Kinki University, was twice higher than the environmental neutron background.