The present invention provides a ready-to-use sterile alginate aqueous solution preparation which is packed in a sealed container or an airtight container and which has storage stability, comprising: (a) a low-endotoxin monovalent metal salt of alginic acid having a weight average molecular weight of 50,000 to 400,000 by a GPC-MALS method; (b) a salt selected from a monovalent metal salt and an ammonium salt; and (c) water, wherein a concentration of the component (a) is 1.5% by mass or more, a concentration of the component (b) is 0.5 to 2% by mass, and a viscosity measured at 20° C. using a rotational viscometer is 2700 mPa·s or more, and a method of producing the same. This alginate aqueous solution preparation is a ready-to-use aqueous solution preparation of a low-endotoxin monovalent metal salt of alginic acid.