This paper reports that the detection to the protein in microarray format is carried out by oblique-incidence reflectivity difference (OI-RD) analysis without any labelling agents. The OI-RD intensities not only depend on the protein structure, but also vary with the protein concentration. The results indicate that this method should have potential application in detection of biochemical processes. The high throughout and in situ detection can be achieved by this method with further improving of the experimental system.