An acid of krypton is formed when krypton tetrafluoride is slowly hydrolyzed by ice at -30 degrees to -60 degrees C. The yield is 2 to 3 percent (mole). A barium salt of this acid, thermally stable at room temperature, is formed by the hydrolysis of krypton tetrafluoride with a 0.35N solution of barium hydroxide at O degrees to 5 degrees C in a yield of approximately 7 percent by weight.