This experiment was conducted to study the internal factors of the apparent difference in fat deposition between Arbor Acres (AA) broilers at the age of 56 days and Beijing-you chickens at the age of 56 and 114 days. One-day-old 60 AA broilers and 120 Beijing-you chickens were randomly assigned to 6 replicates, respectively. The fat deposition, plasma lipid metabolism, concentrations of adipocytokines, enzyme activities, and expression of related genes were investigated. The results showed as follows: the percentage of abdominal fat of AA broilers at the age of 56 days was significantly higher than that of Beijing-you chickens at the same age （P<0.05）, but significantly lower than that of Beijing-you chickens at the age of 114 days （P<0.05）. Beijing-you chickens at the age of 56 and 114 days had higher concentrations of plasma total triglyceride (TG), free fatty acids (FFA) and adiponectin, and activities of plasma lipoprotein lipase (LPL) and hepatic malic dehydrogenase (MDH) than AA broilers at the age of 56 days （P<0.05）. The mRNA expression level of hepatic apolipoprotein A-Ⅰ (apoA-Ⅰ) gene of AA broilers at the age of 56 days was higher than that of Beijing-you chickens at the age of 56 and 114 days （P<0.05）, and adiponectin gene mRNA expression level was higher than that of Beijing-you chickens at the age of 114 days （P<0.05）. Regarding to the abdominal fat, the mRNA expression levels of ATGL and H-FABP genes of AA broilers at the age of 56 days were higher than those of Beijing-you chickens at the age of 114 days （P<0.05）, and A-FABP gene mRNA expression level was lower than that of Beijing-you chickens at the age of 114 days （P<0.05）, and PPARγ gene mRNA expression level was lower than that of Beijing-you chickens at the same age （P<0.05）. There was a positive correlation between A-FABP gene mRNA expression level in abdominal fat and the percentage of abdominal fat （P<0.05）. Positive correlations were also found between the mRNA expression levels of ATGL and PPARα genes in adbdominal fat, apoA-Ⅰ and adiponectin genes in liver, and the mRNA expression level of H-FABP gene （P<0.05）. These results indicate that higher concentrations of plasma TG and FFA induced by higher activities of plasma LPL and hepatic MDH may be one of the reasons of higher fat deposition in Beijing-you chickens. The results also suggest that A-FABP is the key gene that induces the difference of fat deposition between AA broilers and Beijing-you chickens, and H-FABP is the key gene in lipid metabolism pathway. ［Chinese Journal of Animal Nutrition, 2010，22（5）:1334-1341］