A fistula catheter that can prevent separating from the fistula by an inner balloon even if an outer balloon collapses by configuring an internal fixed part with an inner side balloon and an outer side balloon is disclosed. The fistula catheter A has an external fixed part, a supply tube with a primary cavity and a secondary cavity, and an internal fixed part on the tip end side outer periphery of the supply tube, expandable by a compound liquid that includes barium sulfate and distilled water supplied though the secondary cavity. The internal fixed part can be an inner balloon and an outer balloon that communicate with the secondary cavity through filler ports on the peripheral surface of the supply tube. A filter on the filler port can enable distilled water in the compound liquid to be filled into the outer balloon from the secondary cavity through the filter, and the compound liquid can be filled into the inner balloon.