This invention relates to a composition characterized by containing, as essential components, deacetylated chitin and/or a deacetylated chitin derivative, and glyoxylic acid; a solution-containing gel formed from the composition; a water-insoluble chitosan coating; and a material obtained by treating a base material with the composition. According to the present invention, it is possible to provide a chitosan composition, which in a “one-pack” form, has a pot life. Even when dried at room temperature after coating or impregnation of a base material, the chitosan coating can be water-insolubilized with reduced yellowing.