Quantitative phase imaging (QPI) is an advanced optical microscopy technique that requires no sample staining and allows quantitative measurement of biophysical parameters of the cell specimens. This technique is desirable especially in live-cell imaging, as it can yield cellular dry mass distribution, intracellular dynamics as well as size of cells with minimal intervention/damage to the sample. A compact and easily-compatible setup of QPI was developed and applied to a wide range of biomedical applications, ranging from fundamental biological studies in brain imaging, to the clinical studies in drug-screening for breast cancer cells and characterization of pathogenic bacteria biofilms.