Breast cancer is the most common malignancy in women, and surgery is one of the cornerstone treatments for breast cancer. Postoperative pain can significantly reduce patients' quality of life and acute pain may even trigger chronic pain syndrome. Nerve blocks reduces opioid consumption in the postoperative period by providing better pain control and therefore has advantages such as fewer side effects and less risk of pulmonary and cardiac complications. In this study; it was aimed to compare the analgesic effectiveness of serratus posterior superior intercostal plane block and thoracic paravertebral block in the postoperative period in patients who underwent mastectomy.