Background: The use of paravertebral block (PVB) for postoperative analgesia in the thoracic surgery has increased in recent years. However, the traditional methods used to evaluate the success and adequacy of the block are time-consuming, subjective and depend on the patient's compliance. Therefore, the search still continues to find a method to objectively evaluate the success and adequacy of the paravertebral block. Aims: The aim of this study was to investigate whether the Perfusion Index (PI) measured by pulse oximetry technology was an early and quantitative marker for the success of PVB. We also aimed to compare the PI and pinprick method. Methods: The study included a total of 38 patients undergoing elective thoracotomy surgery within the age group of 18-65 years, with class I-II American Society of Anesthesiologists' (ASA) physical status classification. Thoracic PVB was performed for all patients using 20 mL of 5% bupivacaine under ultrasound guidance. After the block was performed, PI measurements were made from the finger and earlobe of the block side for 30 minutes at one-minute intervals. The spread of the block to the anterior chest wall T3-T8 dermatomes was recorded by pinprick sensory test before the block application and fifth, 10th, 15th, 20th, and 30th minutes following the block application. Results: The PI value measured from the finger on the block side increased 1.5 times compared to the baseline value 12 minutes after the block application (p < 0.05). The sensitivity and specificity of PI in determining the success of PVB at 12th minute were 67% and 85%, respectively. Positive predictive value [PPV] was 93% and negative predictive value [NPV] was 75%. The accepted cut-off PI value was found to be 0.84 for a successful PVB. A weak positive correlation was observed between PI and pinprick test (rs = 0.35, P < 0.05). Conclusion: The present study has shown that PI is an objective, fast, practical and non-invasive method, when compare with pinprick method, that can be used to evaluate PVB success.