PBO was invented by air force aerodynamics researchers. At first, the basic patent of polybenzoxazole was held by Stanford University Research Institute (SRI), and later Dow Chemical Company was authorized to industrially develop PBO. At the same time, the synthesis method of original monomer was improved, and the new process hardly produced isomer by-products, which improved the yield of synthetic monomer and laid the foundation for industrialization. 1990 Toyo Textile Company of Japan purchased PBO patented technology from Dow Chemical Company of the United States. 199 1 year, Yi Dao Badish chemical fiber company developed PBO fiber on the equipment of Toyo Textile Company, which greatly improved the strength and modulus of PBO fiber, reaching twice that of PPTA fiber. 1994, Japanese Toyo Spinning Company obtained the license from Yi Dao Badish Chemical Fiber Company, invested a huge sum of 3 billion Zylon to build a spinning production line with 400 tons/year PBO monomer and 180 tons/year, and began to put into partial mechanized production in the spring of 1995. 1998 production capacity reaches 200 tons/year, trade name. According to the development plan of Toyo Textile for Zylon, the production capacity will reach 380 tons/year in 2000, 500 tons/year in 2003 and 1000 tons/year in 2008. Now Toyo Textile in Japan is still the only company in the world that can produce PBO fiber commercially.