Loss of large amounts of DNA probe occurred at the deprotection step of the in situ synthesis of DNA microarrays for analysis of SNPs or gene expression. In this study, we developed "Protected Oligonucleotide Probes" that can avoid elimination of probe DNAs and allow their highly efficient synthesis. The protected oligonucleotide probes containing dC(ac) and d[oxoA(ac)] instead of dC and dA proved to have similar affinity for ssDNA having the complementary sequence and base recognition ability compared with the corresponding unmodified DNA probes.