Microchannel array chips modified by metal deposition or polymer coating were contacted with blood. Titanium (Ti), chromium (Cr) and gold (Au) films were deposited onto the microchannel array chips. Albumin (Alb) and MPC polymer (MPC) were coated onto other chips. Non-treated Si chips were used as a control. Whole blood was collected with 1000 units/ml heparin solution from young healthy volunteers. The passing time of a 100 µl portion of human whole blood through these channels was measured under a pressure difference of 20 cm H2O. Simultaneously, the flow behavior of blood cells in channel was observed by an optical microscope and recorded by a video recorder. Platelet adhesion was observed on Si, Ti, Cr, and especially on Au. The blood pass-through time (BPT) increased in order of Ti, Si, Cr and Au. On the Alb- and MPC-coated chips, platelets were seldom observed and the BPTs were short in comparison with the metal chips. From these consequences, platelet adhesion depended on the materials. The BPT correlated well to the number of adherent platelets on the materials. Therefore, the blood coagulation reaction originated in platelet activation could be detected using microchannel array. We concluded that this method could be applied to evaluate initial blood compatibility of materials within several minutes in vitro.