In order to improve detection speed and accuracy of biological cells, microscopic interferometry which is a noncontact technique for imaging of phase objects is proposed, i.e., red blood cells. The technique combines the principles of off-axis interferometry, confocal microscopy and high-speed image-capture technology and is characterized by optimized spatial resolution and real-time acquisition capabilities. Single carrier-frequency interferogram is captured from experimental setup. According to fast Fourier transform phase retrieval method and path-unfollowing unwrapping algorithm, the quantitative phase distributions of red blood cell are gained and agree well with the previous optical phase models. Analysis shows that the resolution of introduced system reaches sub-micron dimension. It provides a breakthrough method for real-time observing and quantitative analyzing of cells in vivo.