Abstract: NPY plays a significant role in regulating food intake and energy metabolism in teleosts. To understand the biological role of NPY in the silver carp (Hypophthalmichthys molitrix), in this study we determined the full-length cDNA sequence of NPY and investigated the effect of fasting and refeeding on the level of NPY mRNA in the brain and the liver. The full cDNA sequence of NPY consisted of 782 bp, including a 291 bp open reading frame that potentially encodes 96 amino acids, a 68 bp 5'-untranslated region and a 423 bp 3'-untranslated region. Our study on the similarity of the amino acid sequence and the phylogenetic analysis of NPY demonstrated that the NPY gene was relatively conservative during the molecular evolution. The mRNA of NPY was ubiquitously expressed in all the tested tissues and especially abundant in the pituitary. In the brain, the expression of NPY mRNA increased significantly during fasting, and then decreased to the basal level at 6h after refeeding, which indicated that NPY could boost the food intake of the silver carp. In the liver, the expression of NPY mRNA increased significantly until 5d after fasting, then decreased sharply on the 7th day, and finally returned to the basal level at 4h after refeeding. NPY was expressed in a tissue-speci-fic pattern in both the brain and the liver. However, the function of NPY in the liver needs further study. Our study provided insights into the biological roles of NPY in the silver carp.