A novel cyanoimidazole nucleoside and derivative thereof, particularly 4-cyanoimidazolium-5-olate nucleoside and acyl derivatives thereof, and pharmaceutically acceptable salts thereof which are useful as antitumor agents and immunosuppressants, are prepared by dehydrating carboxamide derivatives of the formula: ##STR1## wherein R is an acyl group, and then, if desired, deacylating.