2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is among the most potent environmentally toxic compounds. Serum metabolomics identified azelaic acid-mono esters as significantly increased metabolites after TCDD treatment, due to down-regulation of hepatic carboxylesterase 3 (CES3, also known as triglyceride hydrolase) expression in an arylhydrocarbon receptor (AhR)-dependent manner in mice. The decreased CES3 expression was accomplished by TCDD-stimulated TGFß-SMAD3 and IL6-STAT3 signaling, but not by direct AhR signaling. Methionine- and choline-deficient (MCD) diet-treated mice also showed enhanced serum azelaic acid-mono ester levels following attenuation of hepatic CES3 expression, while db/db mice did not, thus suggesting an association with steatohepatitis. Forced expression of CES3 reversed serum azelaic acid-mono ester/azelaic acid ratios and hepatic TGFß mRNA levels in TCDD- and MCD diet-treated mice and ameliorated steatohepatitis induced by MCD diet. These results support the view that azelaic acid-mono esters are possible indicators of TCDD exposure and steatohepatitis, and suggest a link between CES3, TGFß, and steatohepatitis.