Provided are an optical member including a substrate and a porous layer on the substrate, in which the porous layer includes a silica particle, a silanol group included in the silica particle at a surface of the porous layer is substituted with a functional group included in a divalent organic group having a specific number of atoms and a specific hydrophilic group, and a molar ratio of the divalent organic group to the silanol group on the surface of the porous layer as expressed by the formula of divalent organic group/silanol group is in a range of more than 0.25 and 1.5 or less, an optical instrument including the optical member, and a method for producing an optical member which includes a substrate and a porous layer on the substrate, the method including a coating liquid applying step, a drying and curing step, and an organic chain substituting step.