We describe a method to selectively immobilize a type of leucocytes (neutrophils or eosinophils) from a suspension of mixed leucocytes on the site-specific region inside a microchannel. One of the microelectrodes fabricated at the upper wall of the channel was used for locally electrogenerating hypobromous acid that renders the opposite face of the channel protein-adsorptive. Since the patterned layer of poly(ethylene glycol)dimethacrylate, impervious to HBrO, is previously introduced at the channel bottom, the region of protein adsorption can be precisely defined even in the presence of fluid-flow. After antibody was immobilized on the treated region, an ac voltage (1 MHz, 20 Vpp) was applied to the microelectrodes array in the presence of cell suspension flowing through the channel in order to concentrate cells onto the antibody-immobilized region by negative dielectrophoresis force. The results show that the immobilized antibody would selectively recognize the corresponding leucocyte type from the trapped cells to allow their adhesion.