Marbling score (MS) is the major trait that affects carcass quality in beef cattle. In this study, we investigated the association between genetic polymorphisms of the adipose differentiation-related protein gene (ADFP) and carcass traits in Korean cattle (also known as Hanwoo). Using direct DNA sequencing in 24 unrelated Korean cattle, 25 novel polymorphisms were identified within all exons and their flanking regions of ADFP, including the promoter region (1.5 kb). Among them, 21 polymorphic sites were selected for genotyping in the beef cattle (n = 425). Statistical analyses revealed that one promoter polymorphism (c.-56-18A > G) was associated with MS (P = 0.009). The "A" allele of c.-56-18A > G exerted a lowering effect on MS, e.g., the lowest MS was found in "A/A" (MS = 2.09 +/- 1.23), intermediate in "A/G" (MS = 2.11 +/- 1.31), and the highest in "G/G" (MS = 2.47 +/- 1.47). Our findings suggest that these polymorphisms in ADFP might be important genetic factors involved in carcass quality in beef cattle.