The weatherability and combustibility of fire-retardant-impregnated wood during natural weathering for up to 120 months were evaluated. Fire-retardant chemicals used were modified guanidine phosphate with phenolic additives in order to retain chemicals against leaching. The ability of coating was also examined using four solvent-born coating systems: ① penetrating; semi-transparent（brown）, ② thin-film-forming; semi-transparent（brown）, ③ film-forming; opaque（white）, ④ film-forming; transparent. The systems ① and ② consisted of 2 or 3-coat application of each single coating composition, whereas ③ and ④ employed specific wood-sealers as an undercoat to stabilize the surface of wood prior to the application of topcoat. Before outdoor exposure, the test specimens had about 251kg/m³ of fire-retardant chemicals on average, and their fireproofing performance was equivalent to that of a quasi-noncombustible material. The unpainted test specimens retained the properties of a fire-retardant material after five years, but after 10 years of outdoor exposure, the amount of remaining chemicals had decreased to less than one-tenth, and performance had also declined significantly. All of the painted test specimens had more than 100kg/m³ of remaining chemicals up to five years, and the total heat release was equivalent to that of a quasi-noncombustible material. However, the amount of remaining chemicals continued to decrease thereafter, and after 10 years, the system ④ still had about 100kg/m³ of chemicals remaining, demonstrating fire performance equivalent to a quasi-noncombustible material. However, for the other paints, the amount of chemicals remaining had decreased to 50-70kg/m³, and their fire performance also declined. The system ④ also showed signs of deterioration, such as the coating peeling off, and maintenance was required.