In the study, gas chromatography /time-of-flight mass spectrometry (GC/TOFMS) techniques coupled with principal components analysis (PCA) were used to investigate metabolite perturbations in the serum of the rats exposed to 0.75, 3 or 8 Gy gamma rays.Male standard deviation rats were gamma-irradiated at doses of 0.75, 3 and 8 Gy (1.9 Gy min 21) or sham-irradiated.Serum samples were collected over the first 24 h under the exposure to irradiation in order to analyze the samples by GC/TOFMS.And multivariate data were analyzed by PCA.The composition of metabolites in serum yielded distinct metabolomic phenotypes for 0.75, 3 and 8 Gy at 24 h post irradiation.Nine serum metabolites were significantly altered as a result of radiation exposure.Up-regulated metabolites included inositol, serine, lysine, glycine, threonine and glycerol;down-regulated metabolites included isocitrate, gluconic acid and stearic acid.The nine metabolites were significantly altered afterionising radiation for they may be the potential biomarkers for the diagnosis of radiation injury.