The present invention provides a method for producing a fluorisulfonylimide salt, which enables reducing the impurity content and continuous operation for a long time, and a fluorosulfonyl imide salt. The fluorosulfonyl imide salt of the present invention has a K content of 10,000 ppm or less. The method for producing a fluorosulfonyl imide salt of the present invention is that after a fluorination reaction of chlorosulfonyl imde or a salt thereof, the reaction solution is brought into contact with an aqueous alkaline solution so as to remove impurities. The fluorosulfonyl imide salt of the present invention, in which various impirities are reduced to extremely low levels, is useful as an electrolyte used in a lithium secondary battery, a capacitor or the like, an ionic liquid, or an intermediate for a sulfonyl imide salt, and the like. It is expected that use of the fluorosulfonyl imide salt of the present invention as an electrolyte leads to a high-performance electrochemical device.