Background: Adjuvants like fentanyl and clonidine have found to prolong the duration of analgesia when used along with local anesthetic in the paravertebral space for breast surgery. This study was planned to study the effect of addition of ketamine to bupivacaine for paravertebral block on intra-operative and post-operative analgesia in patient undergoing modified radical mastectomy under general anesthesia. Materials and Methods: This prospective, randomized, controlled double blind study was conducted in 60 women of ASA grade I–III age between 18 to 70 years who underwent modified radical mastectomy. Group A consisted of 30 patients receiving PVB with 0.3 ml/kg of 0.25% bupivacaine and 1 ml normal saline prior to GA and Group B consisted of 30 patients receiving PVB with 0.5 mg/kg ketamine along with 0.3 ml/kg of 0.25% bupivacaine in normal saline prior to GA. Intra-operative supplemental fentanyl consumption, hemodynamic parameter, pain score and post-operative morphine consumption were compared. Results: The mean intra-operative fentanyl consumption requirement in group A was 21.95 ± 21.58 μg, and 12.83 ± 19.93 μg in group B. (p = 0.828) 60% of the patients in group A did not require any analgesic supplementation which was comparable to that in group B (63.33%). First requirement of rescue analgesia in post-operative period was after 3.63 ± 2.55 hr in group A and 3.13 ± 2.84 hr in group B, (p = 0.480). The mean VAS values in both the groups were statistically comparable at rest and as well as on movement. (p > 0.05). Conclusion: The present study, showed that the addition of ketamine to bupivacaine did not improve the efficacy or duration of paravertebral analgesia in the post-operative and intra-operative period in patients undergoing modified radical mastectomy.