In this study, side or toxic effects that may follow the use of thiopentone sodium with or without diazepam in donkeys were observed, through monitoring haematological serum biochemical components of donkeys. This study was conducted using 18 clinically healthy male donkeys, 4-10 years of age, weighing 80-150 kg. The animals were divided to three groups (6 animals of each), and treated with six different protocols containing thiopentone sodium alone (at 10 and 15 mg/kg) or with diazepam (at 0.25 and 0.5 mg/kg). Animals of each group were repeatedly used to study these treatments at interval of 3 weeks from the end of each treatment (as washing period of the drug). They were used alternatively in this study.Some serum biochemical parameters: Total Serum Proteins, Albumin, urea, Glucose, Phosphorus, Aspartate aminotransferase (AST), and alanine aminotransferase (ALT), were evaluated before anaesthesia and at 30, 60, and 90 minutes. Haematological parameters (haemoglobin (Hb), packed cells volume (PCV) and (WBC) count), were recorded. Animals treated with thiopentone sodium at dose rate of 10 mg/kg body weight without premedication resulted in significant increase in haemoglobin (Hb) concentration, while animals subjected to diazepam 0.25 mg/kg and thiopentone sodium 15 mg/kg expressed significant decrease in WBC count. Blood urea nitrogen concentration was significantly increased after anesthesia. Blood glucose was significantly increased; AST and ALT were significantly increased after anesthesia. Animals injected with thiopentone sodium at dose rate of 10 mg/kg body weight exhibited significant (P<0.05) increase in the concentration of serum glucose, serum urea, and ALT level. Increasing the dose of Thiopentone sodium to 15 mg/kg body weight resulted in non-significant (P>0.05) changes in all parameters tested. Animals injected with thiopentone sodium at dose rate of 10 mg/kg + diazepam 0.25 mg/ kg body weight resulted in significant decrease in serum albumin, serum phosphorus, AST, and showed significant (P<0.05) increase in serum ALT. Animals injected with thiopentone sodium at dose rate of 15mg/kg + diazepam 0.25 mg/kg body weight resulted in significant (P<0.05) increase in total serum protein (TSP), and serum ALT. Animals injected with thiopentone sodium at dose rate of 10 mg/kg + diazepam 0.5 mg/kg body weight resulted in significant increase in serum glucose. Animals injected with thiopentone sodium dose rate of 15 mg/kg + diazepam 0.5 mg/kg body weight resulted in significant decrease in serum urea. Conclusion and clinical relevance: increasing the dose of diazepam to 0.5 mg/kg is too toxic to be used with thiopentone at higher doses.