Tramadol is a synthetic, centrally acting opioid analgesic that has the best analgesic efficacy without excessive sedation and significant side effects in the postoperative pain relief in dogs. OBJECTIVES: In this study, hematological and biochemical changes due to short usage of tramadol were assessed in clinically healthy dogs. METHODS: For this purpose, eighteen male mongrel dogs aged 14 to 22 months were used in three equal groups. In the first and second groups respectively (2 and 5 mg/kg) intramuscular tramadol and in control group distillate water was given once a day for five consecutive days. Complete cell blood count (CBC) and biochemical evaluation were done to measure aspartate amino-transferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), creatinin (Cr), and blood urea nitrogen (BUN) levels, before the intervention (day 0) and on days 6 and 13, post-treatment. RESULTS: Thirteen days post treatment, Red blood cell (RBC) and white blood cell (WBC) count and ALT, AST, ALP, Cr, BUN and packed cell volume  (PCV) level was measured as 6.75±0.03, 3.86±0.13, 40.00±7.98, 43.67±8.62, 57.00±17.03, 0.90±0.27, 25.00±5.48 and 40.13±2.88 respect-ively which showed that short-term injection of even high doses of tramadol creates no significant change on hematological, liver, and kidney parameters in dogs. CONCLUSIONS: The present study suggests that tramadol could be a safe postoperative analgesic for control of acute pain in dogs referred for routine surgical procedures.