Purpose: The study aimed to evaluate the analgesic efficiency of dexmedetomidine (DEX) when added to levobupivacaine in continuous ultrasound-guided serratus anterior plane block (SAPB) performed at the end of major thoracic surgery. Methods: This randomized, double-blind trial included 50 adults undergoing thoracic surgery. Continuous SAPB was performed at the end of surgery. Patients were randomized into two groups. Group L (n=25) received levobupivacaine only while Group DL (n=25) received a mixture of levobupivacaine and DEX. All patients received intravenous (IV) paracetamol every 8 hrs. Morphine IV was given according to VAS score of pain as a 5 mg loading dose. The primary outcome measure was postoperative pain intensity. Secondary outcome measures were postoperative morphine consumption and adverse effects. Results: Analgesia was satisfactory in the two groups up to 24 hrs. VAS score was significantly lower in group DL compared to group L between 6 and 24 hrs postoperatively. Total morphine consumption was significantly lower in group DL compared to group L ( p <0.001). Up to 12 hrs postoperatively, sedation score was significantly lower in group DL compared to group L. Afterwards, all patients were fully alert. All values of mean arterial pressure and heart rate were within the clinically accepted ranges. There were no recorded cases of hypotension or bradycardia in the whole studied group. Conclusions: Continuous SAPB with levobupivacaine plus DEX seems to be a promising analgesic alternative following thoracotomy. Combined with IV paracetamol, this approach provided adequate analgesia and proper sedation. Trial registration: ISRCTN registry; study ID: ISRCTN35517318