AIM:To study the inhibitory effect of mononuclear bone marrow cell (BMC) transplantation on carbon tetrachloride (CCIt) -induced liver fibrosis in rats.METHODS:Rat liver fibrosis models were induced by CCN and alcohol administration. After 8 wk,twenty rats were randomly allocated into treatment group (n = 10) and control group (n = 10). BMC were infused into the rats in treatment group via the portal vein,while heparinized saline was infused in control group. CCU was hypodermically injected into the rats twice a week for 4 wk. At the end of wk 12,all rats were humanely sacrificed. Liver samples were taken and stained with HE or Masson trichrome. The general conditions,liver fibrSsis (hydroxyproline and collagen fibre) and liver pathological grades in rats were evaluated.± 128.8μg/g in treatment group,and 596.0 ± 341. 8μg/g in control group.The percentage of collagen fibre was 3.75% ± 0.98% in treatment group and 5.02% ± 0.44% in control group.There was a significant difference berween the two groups (P＜0.05).Liver pathological grade decreased from grade Ⅳ to grade Ⅲ partially in treatment group (P＜0.05) with no obvious improvement in control group (P＜0.05).There was a significant difference between treatment group and control group(P＜0.05).CONCLUSION: Transplantation of BMC can improve liver fibrosis due to chronic liver injury in rats.