Fatty acid synthase (FASN) is an enzyme involved with fat deposition and fatty acid composition in cattle.This study was conducted to detect single nucleotide polymorphisms (SNPs) of the FASN gene and explore their relationships with ultrasound carcass traits in order to assess the potential use of the FASN gene for the breeding selection of Qinchuan cattle for desirable carcass traits.The frequencies of SNP g.12740C>T,g.13192T>C and g.13232C>T were identified in 525 individual Qinchuan cattle which were also assessed for backfat depth,eye muscle area and intramuscular fat by ultrasound.According to the PIC values,g.13192T>C possessed an intermediate polymorphism (0.25T,g.12740C>T possessed low polymorphism (PIC<0.25).Chi-square tests showed that g.13192T>C were in Hardy-Weinberg disequilibrium (c2< c0.052).Two SNPs were found to be associated with variation in ultrasound carcass traits.The H2H2 diplotypes had a greater back fat depth than H1H1,H1H4 andHIH2(P < 0.01).The TT genotype at g.13192T>C was associated with a greater eye muscle area and the TT genotype at g.13232C>T was associated with greater intramuscular fat.When these genotypes were combined there was no difference in eye muscle area and intramuscular fat between the diplotypes.The H2H2 diplotype was associated with carcass traits that are likely to provide economic advantage in Qinchuan cattle.Variations in the FASN genes and their corresponding genotypes may be considered as molecular markers for economic traits in cattle breeding.