The liver and kidney are imperative intentions for the toxicity of drugs, xenobiotics, thymoquinone (TQ) against mercuric chloride (HgCl₂) induced hepatorenal toxicity in rats. HgCl₂ at a dose of 0.02 mg/kg b w injected subcutaneously for 30 days, induced hepatotoxicity which confirmed in this study by increased activity (P ≤0.05) of liver function enzymes; CPK, whereas, serum total protein content and Na⁺-K⁺-ATPase activity were decreased significantly. Herein, HgCl₂ induced also nephrotoxicity; as it induced noticeable signs of renal dysfunctions such as elevated levels (P < 0.05) of serum creatinine, blood urea nitrogen (BUN), uric acid as well as urine N-acetyl glucosaminidase (NAG) activity and total protein content. On the other hand there was a decline in the levels of urinary uric acid; creatinine and creatinine clearance. HgCl₂ induced also oxidative stress in both liver and kidney tissues where reduced glutathione (GSH) content, superoxide dismutase (SOD) and catalase (CAT) activities decreased significantly; increased significantly. Additionally, TGF-β %, CD4% and CD8 % increased significantly in both liver and kidney tissues.  In conclusion: Treatment of TQ concomitantly with HgCl₂ ameliorates effectively the significant changes of all the tested parameters.