Dietary nucleotides reportedly promote functionality and repair in fibrotic liver. Liver fibrosis is characterized by an excessive accumulation of extracellular matrix components, which lead to the impairment of the hepatic function. The aim of this work was to evaluate the influence of dietary nucleotides on liver fibrosis induced by thioacetamide and to elucidate the mechanism by which nucleotides exert their protective effects. Rats consumed ad libitum 300 mg/L thioacetamide in drinking water and were pair-fed diets with (group TN) or without nucleotides (group TS) for 4 mo. Liver histology and extracellular matrix components, liver collagenase and prolyl 4-hydroxylase activities, and tissue inhibitor of metalloproteinases-1 were assessed. The degree of fibrosis was lower in group TN than in group TS. Group TN had lower hepatic concentration of hydroxyproline (P < 0.05), collagen type I (P = 0.12) and type III (P = 0.20), fibronectin (P = 0.05), laminin (P = 0.11) and desmin (P = 0.07), higher collagenolytic activity (P < 0.05), lower prolyl 4-hydroxylase activity (P < 0.05) and lower prolyl 4-hydroxylase (P = 0.10) and tissue inhibitor of metalloproteinase-1 (P = 0.06) expression than group TS. Moreover, expression of tissue inhibitor of the metalloproteinases-1 gene was lower in group TN than in group TS (P < 0.05). These data indicate that the reduction of liver fibrosis in nucleotide-supplemented rats may rely on the enhancement of collagenase activity and the reduction of collagen content and maturation.