Expression of peroxisome proliferator-activated receptor (PPAR) α was investigated in adiponectin knockout mice to elucidate the relationship between PPARα and adiponectin deficiency-induced diabetes. Adiponectin knockout (Adp−/−) mice were generated by gene targeting. Glucose tolerance test (GTT), insulin tolerance test (ITT), and organ sampling were performed in Adp−/− mice at the age of 10 weeks. PPARα, insulin, triglyceride, free fatty acid (FFA), and tumor necrosis factor α (TNFα) were analyzed from the sampled organs. Adp−/− mice showed impaired glucose tolerance and insulin resistance. Additionally, PPARα levels were decreased and plasma concentration of triglyceride, FFA and TNFα were increased. These data may indicate that insulin resistance in Adp−/− mice is likely caused by an increase in concentrations of TNFα and FFA via downregulation of PPARα.