A fuel cell system having an excellent orientation free performance by separating a fluid into a liquid and a gas without being affected by shaking and/or rotation of the fuel cell system includes a fuel cell main body, a first liquid/gas separation unit, and a buffer line. The fuel cell main body receives a fuel containing hydrogen and an oxidizing gas containing oxygen and generates electrical energy through an electrochemical reaction between the hydrogen and the oxygen. The first gas/liquid separation unit is installed on a first recycling line extending from an anode outlet of the fuel cell main body to separate a gas byproduct from unreacted fuel discharged through the anode outlet. The buffer line is fluidly connected to the first and second recycling lines to receive and mix the unreacted fuel and the liquid byproduct at a predetermined amount from the first and second recycling lines, and is further fluidly connected to a third recycling line extending toward an anode inlet of the fuel cell main body to direct the unreacted fuel and the liquid byproduct into the fuel cell main body through the anode inlet.