A solid support for maintaining a uniform spot shape while improving the capacity for immobilization of nucleic acids upon spotting of nucleic acids onto a solid support is provided. A substrate has a base material, an electrostatic layer formed on the base material in order to electrostatically attract nucleic acids, and carboxyl groups formed on the electrostatic layer, wherein the ratio, (COO peak intensity)/(C—C peak intensity) in the C1s spectra obtained by X-ray photoelectron spectrometry (XPS) performed for the surface of the substrate ranges from 0.10 to 0.20. The solid support for immobilizing nucleic acids is produced by active esterification of carboxyl groups of the substrate.