Terrestrial contamination by 137Cs and 134 Cs since 1986 in France is held to originate in atmospheric nuclear weapon tests and/or the releases from the Chernobyl accident. Monthly measurements of radioactivity in terrestrial mosses are part of the monitoring protocol carried out by the Conseil Général of Tarn-et-Garonne to assess the environmental impact of the Golfech nuclear power plant radioactive releases. Since the commissioning of the NPP in 1990, these monthly measurements revealed a contamination by 137Cs and 134Cs (up to 700 and 60 BqKg-1 DW) in both sampling sites. This contamination decreased by a factor about 10 over 1990-2004 through three stages (134Cs undetectable since 1995). It is significantly correlated over large periods of time with the monthly levels of atmospheric halogens-aerosols releases by the Golfech NPP (95%, r2 = 0.35 to >0.84). These results are discussed in the light of the time since radioactive releases, of the operating and release conditions of/from the Golfech NPP and of the mosses sampled. These preliminary results bear evidence of an impact of the Golfech NPP on the terrestrial environment. They confirm that species of terrestrial mosses are particularly sensitive to low levels of atmospheric radioactive caesium contamination and are a good indicator of a radioactive fallout. They suggest that terrestrial mosses may serve to elaborate a predictive model of a caesium release, together with some relevant parameters and in the framework of a carefully defined monitoring protocol.