Object To investigate the effect of PPARα activation on PPARγ-induced fatty liver in the mouse. Methods Wild type mice (C57BL/6) aged 4 to 5 weeks were used as animal models. All mice were divided into four groups. The mice in the first group were fed with chow diet. The mice in the second group were fed with a diet containing 0.125% Wy-14,643, an agonist of PPARa, for 8 days. The mice in the third group were injected with Ad/PPARγ via tail vein for 5 day. The mice in the fourth group were firstly fed with Wy-14,643 diet for 3 days and then injected with Ad/PPARγ via tail vein for another 5 day. Mouse livers were collected and photographed. The effect of PPARα activation on PPARγ-induced fatty liver was observed by H&E and Oil red O staining. Results Compared with the controls, wild-type mice treated with Wy-14,643 for 8 days exhibited marked hypertrophy of hepatocytes with increased cytoplasmic eosinophilia and proliferation of peroxisomes. The liver size was significantly increased in the wild-type mice treated with Ad/PPARγ for 5 days, and over-expression of PPARγ strongly induced hepatic steatosis. Importantly, the wild-type mice pretreated with Wy-14,643 for 3 days and then given Ad/PPARγ injection exhibited dramatically the increase of liver size, which might be due to the dual function of PPARa and PPARγ. Compared with the Ad/PPARγ group, the Wy-14,643 pretreatment group showed a reduced hepatic steatosis. Conclusions Activation of PPARα by Wy-14,643 effectively improves PPARγ-stimulated hepatic steatosis, which provides a novel target for prevention and therapy of fatty liver.