Meat quality has an important genetic component and can be modified by the fatty acid (FA) composition and the amount of fat contained in adipose tissue and muscle. The present study aimed to find genomic regions associated with the FA composition in backfat and muscle (longissimus dorsi) in 439 pigs with three different genetic backgrounds but having the Iberian breed in common. Genome-wide association studies (GWAS) were performed between 38,424 single-nucleotide polymorphisms (SNPs) covering the pig genome and 60 phenotypic traits related to backfat and muscle FA composition. Nine significant associated regions were found in backfat on the Sus scrofa chromosomes (SSC): SSC1, SSC2, SSC4, SSC6, SSC8, SSC10, SSC12, and SSC16. For the intramuscular fat, six significant associated regions were identified on SSC4, SSC13, SSC14, and SSC17. A total of 52 candidate genes were proposed to explain the variation in backfat and muscle FA composition traits. GWAS were also reanalysed including SNPs on five candidate genes (ELOVL6, ELOVL7, FADS2, FASN, and SCD). Regions and molecular markers described in our study may be useful for meat quality selection of commercial pig breeds, although several polymorphisms were breed-specific, and further analysis would be needed to evaluate possible causal mutations. Meat quality depends on the consumer's perception, which is subjected to the socio-demographic backgrounds of the consumer 1 , and is based on factors such as the nutritional value and the organoleptic properties of meat 2. These factors can be modified by the fatty acid (FA) composition and the amount of fat that is contained in adipose tissue and muscle 3. In addition, the consumer is becoming more concerned about the healthfulness of meat 1. Certain saturated FAs (SFAs) raise the cholesterol and low-density lipoprotein (LDL) levels in blood, which increase the risk of suffering a cardiovascular disease 4,5 ; whereas monounsaturated FAs (MUFAs) reduce plasma total LDL-cholesterol without affecting high-density lipoprotein (HDL) levels, which have an anti-atherogenic effect 4,5. Polyunsaturated FAs (PUFAs), especially long-chain omega-3 fatty acids, also reduce LDL-cholesterol levels and the risk of cardiovascular disease 6 , but high amount of PUFAs in meat increase its susceptibility to oxidation, producing meat with undesirable sensory properties 3. In contrast, a high concentration of MUFAs improve meat flavour 7. The Iberian pig is a breed characterized by its great meat quality, due to its high intramuscular fat (IMF) content with an increased proportion of MUFAs (mostly oleic acid) and a reduced quantity of PUFAs 8,9. Conversely, other commercial breeds such as Pietrain and Landrace produce lean meat with a lower proportion of fat,