Abstract: Carbonless copying paper comprising paper coated with microcapsules containing a dye solution which is composed of a solvent, a dye which gives color under acidic conditions and a mineral oil, said dye solution including as solvent one or more of alkylnaphthalenes of the general formula ##STR1## WHEREIN R represents C.sub.1 -C.sub.4 alkyl group, n is an integer of 1-4, and R may be the same or different when n is 2-4, the total number of carbon atoms in R's being 4-6. Such carbonless copying papers exhibit excellent color development and are non-toxic and biodegradable, thus causing no environmental pollution when they are discarded.