Suicidal ideations or attempts in patients with major depressive disorder (MDD) are emergent conditions that require immediate treatment. Numerous therapeutic interventions to reduce suicide risk in psychiatric disorders are effective in long-term suicide prevention, but there is necessity of sufficient, rapid pharmacological treatment of suicidal risk in MDD. Ketamine, an N-methyl-D-aspartate (NMDA) antagonist, has been reported to have rapid antidepressant effect. Depressive symptoms, anxiety, hopelessness, suicidal ideation had decreased within hours after ketamine infusion. Ketamine's rapid symptoms relief and reduction of suicide thoughts has aroused growing interests in psychiatric association.