Abstract Oriented for the quantitative diagnosis of HIV infection status of AIDS patients, a cell biosensor based on electrochemical impedance spectroscopy has been developed for the precise counting of human CD4 + cells. In this new biosensor, the sensing area was composed of densely packed working electrode pixels, each of which was comparable to a single CD4 + cell in size. CD4 + cells were captured on the chemically modified electrode pixels, and detected individually by monitoring the interfacial impedance changes on each independent pixel. The detection of a single cell was achieved by the “on” and “off” states of electrode pixel, depending on the cell capture status. The cell counting was digitalized by summing the electrode pixels in the “on” state (captured with a single cell). Compared with peer counting methods, the biosensor reported here was featured with a small device dimension, a minimal sample consumption, a finest detection resolution and a highest counting accuracy.