A method for treating a radioactive liquid waste containing a sodium salt, which includes: feeding a radioactive liquid waste containing at least one of sodium hydroxide, sodium hydrogencarbonate and sodium carbonate to an anode chamber in an electrolytic cell provided with an anode and a cathode on both sides of a permeable membrane, which is selectively permeable to sodium ions, and electrodialyzing the radioactive liquid waste; separating sodium ions permeated through the permeable membrane as sodium hydroxide from the radioactive liquid waste in a cathode chamber; separating a radioactive substance remaining in the anode chamber as a concentrated radioactive liquid waste; and recovering the separated sodium hydroxide and concentrated radioactive liquid waste, respectively.