Abstract: The aim of the current study was to evaluate the effects of supplementation with N-acetylcysteine （NAC） in the diet on muscle energy metabolism in piglets challenged with lipopolysaccharide (LPS). Eighteen healthy piglets ［Duroc×Landrace×Large white, (11.58±0.26) kg BW］ were randomly allocated to 3 treatments (control group, LPS group and NAC group). Each treatment included 6 replicates with one piglet per replicate. The piglets in the control group and LPS group were fed a basal diet, while the NAC group was fed the basal diet supplemented with 500 mg/kg NAC. On d 10, 13, 14 and 20, the piglets in the LPS group and NAC group were injected intraperitoneally with 100 μg/kg BW LPS, and the piglets in the control group were injected intraperitoneally with the same dose of physiological saline. On d 21, all the pigs were sacrificed to collect gastrocnemius for analysis. The results showed as follows: 1) dietary NAC attenuated the decrease of ATP, total adenine nucleotide (TAN) and energy charge (EC)(P<0.05), while it attenuated the increase of AMP level and AMP/ATP induced by LPS challenge significantly (P<0.05). 2) Dietary NAC attenuated the increase of pAMPK/AMPK induced by LPS challenge (P<0.05). 3) Dietary NAC attenuated the increase of the expression of HSP70 induced by LPS challenge (P<0.05). The results indicate that supplementation with 500 mg/kg NAC in the diet could attenuate the increase of AMP level and AMP/ATP, as well as the decrease of ATP, TAN and EC from LPS challenge. NAC may improve muscle energy status via inhibiting the phosphorylation of AMPK.［Chinese Journal of Animal Nutrition，2011，23（4）：615 -621］