Background: The most common surgical procedure for breast cancer is modified radical mastectomy (MRM), associated with severe acute postoperative pain. With the advent of ultrasonography regional anaesthesia techniques have developed considerably. Present study was aimed to compare dexamethasone and dexmedetomidine as adjuvants for Bupivacaine in ultrasound guided PEC blocks in patients undergoing Modified Radical Mastectomy under General anaesthesia at a tertiary hospital. Material and Methods: Present study was single-center, prospective, clinical study, conducted in patients aged between 18 – 65 years, belonging to ASA Grade l and ll, underwent Modified Radical Mastectomy under General anaesthesia, followed by ultrasound guided PEC blocks. 60 patients were randomly distributed in two groups (30 patients each) by random chit method as group A (Bupivacaine with Dexamethasone) & group B (Bupivacaine with Dexmedetomidine). Results: In present study, 60 patients were divided in group A (n=30) & group B (n=30). General characteristics such as age (years), ASA (I/II), weight (kg), height (cm), BMI (kg/m2), mean duration of surgery (min), baseline heart rate & baseline MAP were comparable among both groups & difference was not statistically significant. In present study, group B (dexmedetomidine) had prolonged duration of analgesia, late requirement of rescue analgesia as compared to group A (dexamethasone), and difference was statistically significant. The VAS pain score was lower in patients of group A as compared to patients in group B up to at 6th postoperative hour and this difference in pain score was statistically significant. Increased incidence of postoperative nausea and vomiting was noted in group B as compared to group A, difference was not statistically significant (p-0.407). Conclusion: Dexmedetomidine has advantages over dexamethasone regarding longer duration of the block and lesser rescue analgesic requirement