In this paper, we investigated how the excavation of ruins and the construction work affected the environmental radiation in the Shikata campus of Okayama University (S-campus). The environmental radiation was steady in the S-campus until 1997, but began to change since 1998, while the ruin's survey and the construction work started frequently after 1998 in the S-campus. In general, the soil and the concrete include the natural radioisotope (uranium series and thorium series, etc). When ruins are surveyed, it is necessary to move a large amount of the soil. In addition, a large amount of the concrete is used for the construction work. To measure the environmental radiation, the monitor posts were set up on the east and west sides of the building of the Radioisotope Center (RIC). We sampled the soil in the container in each place. We used the high-purity germanium detector to analyze them. The monitor posts showed the difference in the in-air dose rate in each place in the S-campus. The in-air dose rate at the east side of the RIC was higher than that at the west side. The result of analysis showed that the soil includes the (40)K at the east side. While the specific activity of the 40K was 0.849Bq/g at the east side, the (40)K was hardly detected in the soil at the west side. The each soil included the 214-lead and 214-bismus ((214)Pb, (214)Bi), however, there was no significant difference in the specific activity of the each soil. The concrete included (40)K, whose specific activity was 0.492Bq/g. It was suggested that the change of the environmental radiation was attributed to radon and its daughter nuclides in the soil rather than the radiation from the concrete in the buildings.