Background: Many environmental insults through accidental discharge, pollution of various kinds, industrial and work place exposure including NBLCO can on exposure inflict dangerous injury on organ and tissue of the body including the liver. And in such cases hepatocellular injury can ultimately cause hepatocellular damage to compromise the synthetic function of the liver as well as liberating ALT and AST to flood the extracellular compartment. A search for cheaper and readily available substance(s) with efficient potentials to ameliorate the harmful effects of these insults is novel. Many herbaceous plants have been reported to possess such property. This study is design to evaluate the ameliorating potentials of Ageratum conyzoides against NBLCO hazardous effects on the liver. Materials and methods: Twenty female Wistar rats (120-150g body weight) were divided into four groups of five rats each. The rats in group I served as the control group and were oral gavaged 3ml/kg of normal saline; group II gavaged 748.33mg/kg body weight of the extract of A. conyzoides, which was 20% of the LD50 (3741.66mg/kg). This dose was calculated as 20% of the lethal dose of 14.14 ml/kg. Group IV animals were gavaged 748.33mg/kg body weight of the extract of A. conyzoides, and 3ml/kg body weight of NBLCO. In all cases, doses were applied daily for 31 days according to animal’s most recent body weight. Results: The results showed that NBLCO significantly increase serum albumin, globulin, ALT, AST and ALP compared with control group (P<0.05). Co-administration of leaf extract of A. conyzoideswith NBLCO caused significant reduction in the aforementioned parameters when compared with crude oil group (p<0.05). Conclusion: It is concluded that ethanol leaf extract of Ageratum conyzoides ameliorates effects of NBLCO in rats.