In this study, we examined the signaling pathways for extracellular signal-related protein kinase (ERK) activation by three structurally different peroxisome proliferator activated receptor-γ (PPARγ) agonists. In murine C2C12 myoblasts, treatment with 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), ciglitazone, and GW1929 leads to ERK1/2 phosphorylation in a time- and concentration-dependent manner. Consistent with ERK phosphorylation, mitogen activated protein/ERK kinase (MEK) phosphorylation as well as Raf-1 kinase activity are also accordingly stimulated, while the constitutive Ser259 phosphorylation of Raf-1 is decreased. The ERK phosphorylation induced by PPARγ agonists is not blocked by the PKC inhibitors GF109203X and Ro31-8220, the PI3K inhibitor wortmannin, the Ras inhibitor FPTI, the negative mutant of Ras, or the PPARγ antagonist bisphenol A diglycidil ether. Expression of PPARγ2 without DNA binding domain or with a nonphosphorylatable mutant (S112A) fails to change ERK phosphorylation by 15d-PGJ₂. On the contrary, the ERK phosphorylation by PPARγ agonists is inhibited by the MEK inhibitor PD98059, GSH, and permeable SOD mimetic MnTBAP. Chemiluminescence study reveals that these three PPARγ agonists are able to induce superoxide anion production, with an efficacy similar to their action on ERK phosphorylation. Consistent with this notion, we also show that superoxide anion donor 2,3-dimethoxy-1,4-naphoquinone elicits ERK phosphorylation. In this study, we for the first time demonstrate a novel mechanism, independent of Ras activation but initiated by superoxide anion production, for PPARγ agonists to trigger the Raf-MEK-ERK1/2 signaling pathway.