Background &Aims: Erector Spinae Plane (ESP) block has been proven to be an effective component of multimodal analgesic regimens for breast surgeries with fewer side effects. Here, we aimed to compare the analgesic efficacy of two different concentrations of levobupivacaine in ultrasound guided ESP block for breast surgery in terms of duration, quality of analgesia and postoperative analgesic consumption. Methodology: This prospective randomized comparative trial was done on 60 adult female patients aged between 20-65 years who were scheduled for unilateral modified radical mastectomy and randomly divided into two groups (30 each). In group A, 0.25% levobupivacaine and in group B, 0.375% levobupivacaine in same volume (20 mL) was given in ultrasound (US)-guided ESP block. Duration, quality of analgesia and adverse effects were noted. Statistical analysis was performed using student’s t-test and chi-square test. Result: The duration of analgesia was significantly prolonged in group B as compared to group A (907.7 ± 53.8 minutes and 711 ± 68.9 minutes respectively). The postoperative VNRS scores remained persistently less than 3 in both the groups except at 12th hours in group A and 18th hours in Group B. Postoperative rescue analgesic consumption was also higher in Group A (230 ± 46.6 mg) as compared to Group B (136.7 ± 49.0 mg). Conclusion: Although use of both concentrations of levobupivacaine (0.25% and 0.375%) in ESP block can provide effective postoperative analgesia but the 0.375% levobupivacaine has significantly prolonged analgesia and lesser postoperative analgesic consumption without any significant adverse effects in unilateral breast surgery.