We developed a novel silanized flat and smooth mica substrate that can fix and straighten DNA using meniscus force. Producing the substrate was achieved by methyltrimethoxysilane-coupling of the freshly cleaved mica surface. The silane-coupled substrate had an extremely flat surface with a root-mean-square (rms) roughness of only 0.09 nm, and was able to fix DNA very straightly on its surface. Moreover, the height of the fixed DNA was about 1.1 nm by atomic force microscopy (AFM), higher than those reported in previous studies. Thus, the straightening process of the DNA on this substrate caused little structural distortion of the double stranded DNA. The substrate will be effective for investigating the biomaterials, such as DNA and/or protein by AFM and scanning near-field optical microscopy (SNOM or NSOM).