Acetaminophen is commonly used in veterinary practice and it is known to produce hepatotoxicity at high doses especially in companion animals. Silybon 140® (Silybum marianum) is a new drug for the treatment of several liver injuries in humans. This experiment investigated the protective effect of Silybon 140 on toxicities induced by acetaminophen in dogs. Twelve Nigerian dogs about 12 months of age were randomly separated into four groups of three dogs each. Group 1 received only distilled water throughout the experiment while groups 2 and 3 were administered Silybon 140 at dose of 100 and 200 mg/kg for three days respectively.  A day after, groups 2, 3 and 4 were administered acetaminophen at dose of 500 mg/kg once. All medications were given orally. Blood samples were collected in two samples bottles; one with EDTA and the other without EDTA for hematology and serum biochemistry studies. Blood samples were collected before drug administration and at day 7, 14 and 21 post acetaminophen administration. The results showed significant protective effect of Silybon 140 on the liver and kidney against acetaminophen toxicity. At day seven there was significant decrease in AST levels in Silybon treated groups and ALT levels at day 21 comparing to acetaminophen group. Similarly, creatinine levels of 1.7±0.1, 1.6±0.3 and 2.7±0.3 for groups 2, 3 and 4 respectively were observed. At the doses of 100 and 200 mg/kg, Silybon 140 effectively protected the liver and kidney against acetaminophen induced renal and hepatic toxicity, thus can be used for disease conditions affecting the liver and the kidney in dogs.