Introduction: The ultrasound (US)-guided erector spinae plane (ESP) block is a new regional anesthetic technique that offers significant advantages over paravertebral block as it is easy and safe to perform. We aim to compare the efficacy of US-guided paravertebral block with ESP block for postoperative analgesia in modified radical mastectomy (MRM). Methods: Eighty female patients of age group 18–70 years, belonging to physical status American Society of Anesthesiologists (ASA) I and II, undergoing MRM were included in the study. In Group P, patients received paravertebral block and in Group E, patients received ESP block before induction of general anesthesia. Both the groups received 0.5% 20 mL ropivacaine. The time to first rescue analgesia and total doses of rescue analgesics were recorded in the postoperative period. Numeric Rating Scale (NRS) scores at 0 min, 30 min, 1 h, 2 h, 6 h, 12 h, and 24 h were noted, and patient satisfaction was evaluated at 24 h. Unpaired t-test or the Mann–Whitney U test was used to compare quantitative variables while Chi-square test or Fisher's exact test was used to compare qualitative variables. Results: The time for the first analgesic request was 232.5 min (140-1200) in ESP group as compared to paravertebral group in which the duration was 205 min (135-1190) (P value = 0.29). The total dose of rescue analgesics and NRS scores in postoperative period were comparable. However, the time to perform ESP block was significantly shorter than that of paravertebral block. Conclusion: ESP block can be used as a safe and easy to perform alternative analgesic technique over paravertebral block in breast cancer surgeries.