Postmortem brain analysis and PET imaging analysis are two major methods to estimate microglial activation in human subjects, and these studies have suggested activation of human microglia in the brain of patients with various neuropsychiatric disorders. However, by using the above methods, only limited aspects of microglial activation can be measured. We have originally developed a technique to create directly induced microglia-like (iMG) cells from fresh human peripheral blood monocytes adding GM-CSF and IL-34 for 2 weeks, instead of brain biopsy and iPS technique (Ohgidani, Kato et al. Sci Rep 2014). Using the iMG cells, dynamic morphological and molecular-level analyses such as phagocytosis and cytokine releases after cellular-level stress exposures are applicable. Just recently, we have confirmed the similarity between human iMG cells and brain primary microglia by RNAseq (Tanaka, et al. Front Immunology 2021). We believe that patients-derived iMG cells will take a role as one of the important surrogate markers to predict microglial activation in human.