Ketamine is an important component of multimodal treatment and a commonly used anesthetic drug. However, its analgesic effects have not been fully assessed intraoperatively because of difficulties in measuring this effect. In this case report, a woman underwent general anesthesia with ketamine and its pupillary reflexes were measured to detect autonomic changes in response to pain. With increasing doses of ketamine, the pupillary light reflex and the pupillary dilation response decreased. This could be caused by N-methyl-D-aspartate receptor antagonism in the pupillary reflexes pathway or by the analgesic effects of ketamine.