A biomarker is defined as a biological indicator of normal or pathological processes, and a pharmacological response to a therapeutic intervention, whose characteristics can be measured and evaluated objectively. In medicine and health, biomarkers can be paraphrased as diagnostic methods objectively conducive to treatment. Here, we discuss biomarkers of schizophrenia as a representative mental illness, whose research has advanced compared with that of other disorders. Schizophrenia is a syndrome with a typical course and symptoms. Its pathophysiology and pathogenesis have not been elucidated (medically however, its underlying biological mechanisms are assumed to be present. That is, in biomarker discovery, when the pathogenesis and cause are elucidated, the patient group would not consiste of schizophrenia but, it is a new disease of "x x disease." For example, neurosyphilis is exogenous psychosis, by finding a biomarker of syphilis spirochete, a new disease concept of neurosyphilis could be distinguished from the schizophrenia). In this way, it can be said that biomarker research is essential for the development of new diagnostic and treatment methods for mental illness. There are several biomarker research methods such as genetic analysis, biological sample analysis, cognitive analysis, neurophysiology, neuroimaging, animal models, and post-mortem brain analysis. Further, studies have been made, however, biomarkers that can explain all of schizophrenia has not been found yet. As schizophrenia is assumed to be a heterogenous syndrome, it is believed that the etiology varies. Thus, there is a possibility that targeting schizophrenia as a whole will make it difficulty to find biomarkers for patients with schizophrenia. It is considered that appropriate subgroup analysis is needed. In order to overcome it, amount-of-resources strategy to find patients by using large of samples has been made mainly in Europe and the United States. In Japan, we have used sub-group analysis strategy to elaborate this issue such as the use of an intermediate phenotype. It is not possible to research a similar strategy, because of the limited funds and manpower in Japan compared to U. S. and Europe. As nationwide research organizations in Japan, such as IGC (Imaging genetics consortium), combination analysis of genetics and neuroimaging and COCORO (Cognitive genetics collaborative research organization), combination analysis of genetics and cognitive function, have been established, the development of biomarkers for mental illnesses is expected in the near future.