Abstract: The experiment was conducted to investigate the effects of lipopolysaccharide (LPS) on PPARγ mRNA expression in the peripheral white blood cells, thymus, spleen and intestinal lymphoid node of weanling piglets. 12 pigs were divided into two groups (6 replicates/treatment and 1 pig/replicate). The piglets in the treatment group were injected intraperitoneally with 100 μg/kg BW LPS, whereas pigs in the control group were injected with an equivalent amount of sterile saline. Blood samples were collected at 1.5 and 3 h post-challenge for isolating plasma or white blood cells. Following blood collection at 3 h, the piglets were slaughtered to collect thymus, spleens and intestinal lymph node for detection. The results showed that: (1) Tumour necrosis factor-α and cortisol were increased significantly 1.5 and 3 h after LPS challenge (P<0.001), insulin was decreased significantly (P<0.001), and glucogan was increased significantly (P<0.001) 3 h after LPS challenge. Additionally, LPS challenge changed blood biochemical parameters significantly. These results indicate that LPS challenge induces acute immunological stress in piglets. (2)LPS challenge increased PPARγ mRNA expression in the peripheral white blood cells (P<0.001), thymus (P<0.05) and intestinal lymphoid node (P<0.05), which indicates that immunological stress induced PPARγ mRNA expression of immune cells and immune organs. These results suggest that PPARγ may play an important role in regulation of immunological stress in pigs, and may be a new target for alleviating immunological stress of piglets.