Abstract: ApoB (apolipoprotein B), as the carrier of triglyceride, plays an essential role in the transport and metabolism of energy. So it was studied as one of the main candidate genes for growth and body composition traits. To discuss the relationship of apoB gene with growth and body composition traits especially for fatness in chicken, the eighth generation divergent lines of lean and fat broilers bred by Northeast Agricultural University were used in the present study. A SNP (T→G) in exon 26 of apoB gene, named T123G, was discovered by sequencing. Association analysis indicated that this SNP significantly related to body weight of 1, 3 week of age, abdominal fat weight and abdominal fat percentage at 7 week of age (P<0.05). Multicontrast analysis indicated that the birds with genotype GT were significantly higher than those with genotype GG for body weight at 1 week of age, the birds with genotype TT or GT were significantly higher than those with genotype GG for body weight at 3 week of age, and the birds with genotype TT were significantly higher than those with genotype GT or GG for abdominal fat weight and abdominal fat percentage. Population genetic analysis indicated that the frequencies of the three genotypes were significantly different in the two lines (P<0.05). So we putatively drew the conclusion that apoB or a tightly linked gene has important effects on body weight and deposition of abdominal fat in the chicken.