A fluidized bed boiler plant and a method of preheating combustion gas in a fluidized bed boiler plant. The boiler plant includes a furnace and a combustion gas channel, and a water-steam cycle including an evaporator section, a superheater section including a last superheater and a steam turbine, and a superheating path for conveying steam from the evaporator section via the superheater section to the steam turbine, and a first combustion gas preheater. The fluidized bed boiler plant includes a second combustion gas preheater, a steam extraction line attached in flow connection with the second combustion gas preheater and with the superheating path in a location upstream of the last superheater for conveying steam from the superheating path to the second combustion gas preheater.