The two-side writing fountain pen of the present invention comprises an ink output means and a holding means which is provided for fastening the ink output means, and said ink output means includes a pen nib member and a feed member. The pen nib member includes a pen nib flake and a pen tip granulation element formed at the tip of the pen nib flake, wherein the pen tip granulation element is formed with a pen tip front contact section, a pen tip back contact section and an ink output passage communicating with the pen tip front contact section and the pen tip back contact section, and then the pen nib flake is provided with an ink guiding passage communicating with the ink output passage. The feed member includes an ink input section and an ink output section, said ink input section is provided within the holding means, and the ink output section connects with the ink guiding passage of the pen nib flake.