The effect of the medicinal herb Rosemary (Rosmarinus officinalis) with or without trichloroacetic acid (TCA) on the histological structure of liver of Swiss albino mice and on some liver function tests was investigated. Eighty female mice 20-26gm were divided into 4 groups; control group, group treated with TCA 500 mg/kg body weight in drinking water, group treated by oral gavage with 0.1ml aqueous extract of Rosemary 60 mg/kg and group treated with TCA and Rosmarinus officinalis for 3 weeks. Mice treated with TCA showed loss of appetite, loss of body furs and decreased activity. These alterations decreased in mice administrated Rosmarinus officinalis and TCA. Final body weight of mice treated with TCA exhibited a significant decrease in comparison with control group. An improvement in weight was recorded in mice treated with Rosmarinus officinalis and TCA. Treatment with TCA, led to a significant increase in serum alanin aminotransferase (ALT) and insignificant increase in aspartate aminotransferase (AST) and total protein. Administration of Rosmarinus officinalis with TCA inhibited the elevation of ALT but not the elevation of AST or total protein. Liver sections of TCA treated group illustrated congestion of central veins with hemolysis and loss of normal architecture with prominent Kupffer cells. Some hepatocytes exhibited slight hypertrophy. Focal necrotic areas associated with inflammatory cells infiltration and vacuolation of hepatocytes were obvious. Histochemical examination revealed. increased reactivity of hepatocytes with periodic acid Schiff technique (PAS). In mice treated with Rosmarinus officinalis and TCA; most pathological lesions disappeared and hepatocytes showed reactivity to PAS close to that of control group.