Background and aims Dexmedetomidine has been noticed to be safe and efficient in prolonging the duration of peripheral nerve blocks. This study was designed to compare the length, quality of postoperative analgesia, hemodynamic stability, and patient’s satisfaction and number of patients requiring analgesia with the addition of dexmedetomidine to bupivacaine versus plain bupivacaine in pectoral nerve block (pecs) for modified radical mastectomy (MRM). Patients and methods These patients were randomly allocated using a computerized random number generator into two groups: group I (control group) (30 patients) received 25 ml of 0.25% of plain bupivacaine that was used for modified pecs block. Group II (study group) (30 patients) received 25 ml of 0.25% of plain bupivacaine plus dexmedetomidine (Precedex) 1 μg/kg that were used for pecs block. Results The results showed a longer duration of analgesia in group II (21±3 h) in comparison with group I (16±4 h). Statistical analysis showed a statistically highly significant (P=0.006). Also, consumption of morphine was lower in group II (5±3 mg/24 h) in comparison with group I (9±4 mg/24 h). Statistical analysis showed a statistically significant (P=0.01). Conclusion Dexmedetomidine as an adjunct to bupivacaine helps increase the duration and improves the quality of postoperative analgesia in pecs block without serious side effects.