CAR-T cell immunotherapy is a promising therapeutic modality for cancer patients. The success of CAR-T cell therapy has been associated with the phenotype, activation and functional profiling of infused CAR-T cells. Therefore, immunophenotypic characterization of CAR-T cells during bioprocess is crucial for cell quality control and ultimately for improved antitumor efficacy. In this chapter, we propose a flow cytometry panel to characterize the immunophenotype of the CAR-T subsets.