Social stress can cause or exacerbate neuropsychiatric illnesses such as depression. Unfortunately, currently available treatments for these disorders are slow to take effect and are often ineffective. One promising novel treatment option is the anesthetic ketamine, which may have rapid-acting antidepressant effects in humans and rodents. These rodent studies, however, have primarily used artificial stressors to produce depression-like responses. Our lab uses an ethologically relevant rodent model of social stress in Syrian hamsters. We tested whether a single, intraperitoneal dose of ketamine reduces social avoidance, a common symptom of mental disorders, in male and female Syrian hamsters that have experienced social stress. Social avoidance was tested one day after ketamine injection. Eight days later, subjects were defeated again, and tested for avoidance the following day. Ketamine reduced avoidance one day but not nine days post-injection. These data suggest that ketamine can act rapidly to prevent depressive-like responses to social stress.