The coronavirus disease 2019 (COVID-19) pandemic continues to spread around the world, and widespread vaccination is considered the most effective way to end it. Although the efficacy of COVID-19 vaccines has been confirmed, their safety remains a concern. In this paper, we report two cases of ruptured vertebral artery dissecting aneurysm (VADA) immediately after messenger RNA (mRNA) anti-COVID-19 vaccination. In Case 1, a 60-year-old woman experienced sudden headache 3 weeks before her first dose of the Moderna mRNA-1273 COVID-19 vaccine. Magnetic resonance imaging showed dilatation of the right vertebral artery (VA) without intracranial hemorrhage. A day after the vaccination, she developed subarachnoid hemorrhage with pulmonary effusion due to a ruptured right VADA. She underwent endovascular internal trapping and parent artery occlusion under general anesthesia. In Case 2, a 72-year-old woman with a previous history of the left VA occlusion due to arterial dissection developed subarachnoid hemorrhage 7 days after the first dose of the Pfizer-BioNTech BNT162b2 COVID-19 mRNA vaccine due to a ruptured right VADA and underwent stent-assisted coil embolization under general anesthesia. The postoperative courses of these two cases were uneventful. The accumulation of more cases and further study are warranted to clarify the relationship between COVID-19 mRNA vaccination and ruptured intracranial dissecting aneurysms.