Adsorption of phosphorus on a denitration catalyst degrades the activity of the catalyst during long-term operation of coal-fired power plants. In order to remove phosphorus and to regenerate a spent catalyst from a real coal-fired power plant, leaching behavior with water and ammonium citrate solution was investigated and change of the catalytic activity was observed. When the catalyst was treated with ammonia citrate, 67% of phosphorus could be removed, and the activity was recovered by restoration of ammonia adsorption capacity. A part of phosphorus (29%) was removed by leaching with distilled water, whereas negligible change in activity was observed.