Long-term results and experience of 15 year operation of NH3 synthesis plant in Nitrogen Works Kedzierzyn Ltd. (prodn. capacity 1500 t/d) were presented. The plant was designed and erected by Polish companies and started up in January 1993. A newly designed Polish PS3-INS catalyst was applied in INS-21 type prototype reactor On 11th November 2007, the 5 000 000-th NH3 ton was produced on the catalytic load after almost 15 years of plant operation. Only 3 harmless failures of the plant were noticed in this period.