Abstract Objective To compare the analgesic effect of intercostal nerve block (INB) with ropivacaine when given preventively or at the end of the operation in patients undergoing video-assisted thoracic surgery (VATS). Methods A total of 50 patients undergoing VATS were randomly divided into two groups. The patients in the preventive analgesia group (PR group) were given INB with ropivacaine before the intrathoracic manipulation combined with patient-controlled analgesia (PCA). The patients in the post-procedural block group (PO group) were administered INB with ropivacaine at the end of the operation combined with PCA. To evaluate the analgesic effect, postoperative pain was assessed with the visual analogue scale (VAS) at rest and Prince Henry Pain Scale (PHPS) scale at 6, 12, 24, 48, and 72 hours after surgery. Results At 6 h and 12 h post-surgery, the VAS at rest and PHPS scores in the PR group were significantly lower than those in the PO group. There were no significant differences in pain scores between two groups at 24, 48, and 72 hours post-surgery. Conclusion In patients undergoing VATS, preventive INB with ropivacaine provided a significantly better analgesic effect in the early postoperative period (at least through 12 h post-surgery) than did INB given at the end of surgery.