Systemic metabolic effects and toxicity mechanisms of ambient fine particulate matter(PM2.5)remain uncertain.In order to investigate the mechanisms in PM2.5 toxicity,we explored the endogenous metabolic changes and possible influenced metabolic pathways in rats after intratracheal instillation of PM2.5 by using a 1H nuclear magnetic resonance(NMR)-based metabolomics approach Liver and kidney histopathology examinations were also performed.Chemical characterization demonstrated that PM2.5 was a complex mixture of elements.Histopathology showed cellular edema in liver and glomerulus atrophy of the PM2.5 treated rats.We systematically analyzed the metabolites changes of serum and urine in rats using 1H NMR techniques in combination with multivariate statistical analysis.Significantly reduced levels of lactate,alanine,dimethylglycine,creatine,glycine and histidine in serum,together with increased levels of citrate,arginine,hippurate,allantoin and decreased levels of allthreonine,lactate,alanine,acetate,succinate,timethylamine,formate in urine were observed of PM2.5 treated rats.The mainly affected metabolic pathways by PM2.5 were glycine,serine and threonine metabolism,glyoxylate and dicarboxylate metabolism,citrate cycle(TCA cycle),nitrogen metabolism and methane metabolism.Our study provided important information on assessing the toxicity of PM2.5 and demonstrated that metabolomics approach can be employed as a tool to understand the toxicity mechanism of complicated environmental pollutants.