Sox6, a fast myofiber-enriched repressor of slow muscle gene expression, plays an important role in the control of skeletal muscle fiber-type transition. Mammalian Sox6 has been isolated and characterized from mice, rats, and humans. In this study, the porcine Sox6 (pSox6) cDNA was cloned by degenerate PCR. The entire open reading frame (ORF) of pSox6 is 2406 bp. The predicted protein is composed of 801 amino acids and contains the HMG box, leucine-zipper motif, and glutamine-rich Q-box. The amino acid similarities between the Sox6 from pig and other mammals range from 90% to 95%. Real-time quantitative PCR analysis indicated that pSox6 mRNA was most abundant in the heart and skeletal muscles. Overexpression of pSox6 led to downregulation of myosin heavy chain (MyHC) I expression and upregulation of MyHC IIa, MyHC IIx, and MyHC IIb expressions. This is the first report on molecular cloning and characterization of porcine Sox6.