There are no reports regarding pneumomediastinum caused by thoracic epidural block complications. We believe that it is possible to experience an occurrence of pneumomediastinum caused by air in the epidural space after performing a thoracic epidural block using the loss of resistance (LOR) technique with air. We report a witnessed case where pneumomediastinum appeared after a thoracic epidural block. Pneumorrrhachis, paravertebral muscle emphysema, and pneumomediastinum were diagnosed by Positron Emission Tomography-Computed Tomography. Although extremely rare, pneumomediastinum can be caused by an epidural block using LOR technique with air. In order to avoid the above danger, the use of saline or very minimal amount of air is required during a careful LOR technique.