Melanocortin-4 receptor (MC4R) is a member of the superfamily of G-protein-coupled receptors (GPCRs), which affects body weight, energy homeostasis and food intake in humans and mice. In this study, the Asp298Asn polymorphism of the MC4R gene was investigated in Laiwu, Yorkshire×Laiwu and commercial cross-bred pig populations using polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP), and the relationship of this mutation with backfat thickness was analysed. The results indicated that only genotype 11 exists in 33 individuals of Laiwu pigs, and three genotypes (11, 12 and 22) were detected in Yorkshire×Laiwu and commercial cross-bred populations. The distributions of allele and genotype frequencies in Yorkshire×Laiwu and commercial cross-bred populations were similar, with the frequency of allele 1 being higher than that of allele 2. In commercial cross-bred pigs, the mean backfat thickness of individuals with genotype 22 was significantly higher than that of individuals with genotypes 12 (P<0.01) and 11 (P<0.05). This study provides evidence that the Asp298Asn polymorphism of the MC4R gene is associated with backfat thickness in commercial cross-bred pigs with Western pigs as parental lines and, therefore, can be used as a DNA marker for breeding in such populations of pigs.