An injection nozzle assembly for a fuel cell system, the injection nozzle assembly including a housing defining a fuel chamber to accommodate hydrogen-containing fuel therein and coated with a reforming catalytic layer. An inlet is provided in a first side of the housing to introduce the hydrogen-containing fuel in the fuel chamber and an outlet is provided in a second side of the housing to discharge the hydrogen-containing fuel from the fuel chamber. An injection means is provided in the fuel chamber so that noise, vibration and power consumption due to operation of a fuel pump are reduced, and transformation efficiency for producing hydrogen ions and electrons from the hydrogen-containing fuel is increased.