Abstract: An aqueous treatment composition for cellulosic material comprises an aqueous fire retardant solution of urea (CO(Na2)2, a source of inorganic acid groups such as phosphoric acid, monoammonium phosphate or diammonium phosphate, a water miscible alcohol such as methanol or ethanol, and an inorganic borate, typically a mixture of boric acid and borax pentahydrate. The treatment composition may be provided in a concentrated or water-free form, in which case the treatment composition is formulated into an aqueous fire retardant and preservative solution at the point of use. The treatment composition can be prepared from a kit containing the various components in two separate containers. Also provided is a method of simultaneously improving the resistance to heat and/or fire and preserving a cellulosic material comprising treating the cellulosic material with a treatment composition of the invention.