Ketamine is commonly used in the emergency department for procedural sedation. It is the most commonly chosen sedative drug in children because of its rapid onset, short half-life, little respiratory depression, and can be administered intravenously and intramuscularly. Common side effects include hallucination, visual disturbance, dizziness, nausea, and vomiting. Recently, it has also been used as an anticonvulsant for refractory status epilepticus. The authors encountered a case of generalized tonic-clonic seizure in a four-year-old boy after an intramuscular injection of ketamine for procedural sedation. This case is reported to share the author’s experience with medical professionals who use ketamine and raise awareness.