A silicon nanosheet comprising a silicon atom layer formed by bonding two-dimensionally and periodically arranged silicon atoms to each other through an Si—Si bond. A nanosheet solution prepared by dispersing or suspending the silicon nanosheets in a solvent. A nanosheet-containing composite having the silicon nanosheets on the surface and/or in the interior of a substrate. A nanosheet aggregate formed by aggregating the silicon nanosheets. A process for producing a nanosheet solution comprising: an acid treatment step of bringing a layered silicon compound into contact with an aqueous acid solution to derive a siloxene compound; and an exfoliation step of adding the siloxene compound into a solvent containing a surfactant, shaking the mixture, and peeling off the siloxene compound.