Abstract: A method of producing a standard seawater solution for nutrient salt measurement includes at least: an impurity removal treatment step (S2) of removing an impurity from a seawater sample containing a nutrient salt; a main sterilization treatment step (S4) of killing a microorganism in the seawater sample; a bottling step (S6) including pouring the treated seawater sample into a resin bottle (3) and hermetically sealing the resin bottle; and a metal sealing step (S7) including covering an outer surface of the resin bottle (3) after the hermetic sealing with a film-like material (5) including a metal film (or a metal foil) (5a) and sealing the resin bottle therein by reduced pressure suction.