Several cellular events cause permanent or transient changes in intrinsic magnetic and density properties of cells. Characterizing these changes in cell populations is crucial to understand cellular heterogeneity in cancer, immune response, infectious diseases, drug resistance, and evolution. For such biological characterization and monitoring changes in cellular properties, our group has developed a density-based cell characterization/sorting platform that employs the principle of magnetic levitation (MagLev) (Fig. 1A). Using the platform, we have demonstrated that changes in cellular density to environmental stressors can be monitored in real time at the single-cell resolution based on the levitation profile within the device (Fig. 1B). Our MagLev technologies have been further applied to (i) counting cells by integrating it with a smartphone-based portable imaging system (i-Lev) (Fig. 2), (ii) monitoring cellular responses to a drug or toxicant at home settings, and (iii) isolation of circulating tumor cells/clusters via microfluidic integration.