Transforming growth factor-beta1 (TGF-beta1) is an important mediator of tissue fibrosis, including liver cirrhosis. Ribbon-type antisense oligonucleotide to TGF-beta1 (TGF-beta1 RiAS) was designed and combined with cationic peptide derived from the nuclear localization signal of human immunodeficiency virus-1 Tat protein for enhanced cellular uptake. When Hepa1c1c7 cells were transfected with TGF-beta1 RiAS, the level of TGF-beta1 mRNA was reduced by >70%. TGF-beta1 RiAS, mismatched RiAS, and normal saline were each injected into mice via the tail vein, beginning the week after intraperitoneal CCl4 injection and continuing for 7 weeks, in order to determine whether TGF-beta1 RiAS prevents the fibrotic changes induced by the CCl4 injection. After 8 weeks of the experiment, all of the mice treated with TGF-beta1 RiAS survived, compared to 50% of the control group and 65% of the mismatched RiAS-treated group. Upon examining the biochemical effects on the liver, TGF-beta1 mRNA levels were reduced significantly only in the TGF-beta1 RiAS-treated group. Immunohistochemical studies showed a reduced accumulation of collagen and alpha-smooth muscle actin. Our experimental results suggest that ribbon antisense to TGF-beta1, with efficient uptake, effectively blocks the expression of TGF-beta1 and prevents fibrosis of the liver.