Major depressive disorder (MDD) is one of the world′s major chronic and disabling mental diseases.2030, MDD is expected to be the top of all the disease burden in the world, with high prevalence, high recurrence rate, high disability rate, and high suicide rate. Suicide is the most serious consequence of MDD. Current studies showed that inflammatory levels in the central nervous system and peripheral blood of patients with MDD were higher, and increased more significantly in depressive patients with suicidal ideation or behavior. Related researches showed that increased levels of inflammatory cytokines were associated with dysregulation of kynurenine metabolic pathway, leading to imbalances in neurometabolites, such as an excess of the neurotoxic product quinolinic acid and a decrease in the protective neuropeptide picolinic acid. This paper reviews kynurenine metabolic pathway, expecting to identify the biomarkers of MDD patients with suicide.