To investigate MT 1 MMP mRNA expression in the development of liver fibrosis and during the reversal of liver fibrosis ,we undertook a dynamic observation by situ hybridization. Liver fibrosis model was established by intraperitoneal injection with CCl 4 in Wistar rats, then allowed them fo recover spontaneously to observe the reversal of liver fibrosis .The results showed that MT 1 MMP mRNA was expressed mainly in mesenchymal cells(such as hepatic stellate cell), also in a part of hepatocytes.The levels of MT 1 MMP mRNA expression were increased gradually in the development of liver fibrosis and decreased gradually during reversal of liver fibrosis. These results suggest that the expression of MT 1 MMP may have an important role in the development of liver fibrosis and its reversal.