This invention relates to a water-soluble fiber and a method of manufacturing the fiber. The water-soluble fiber of the invention is composed of a high molecular compound with a weight average molecular weight of not less than 10,000, which high molecular compound is obtainable by reacting a polyalkylene oxide compound, which is obtainable by addition polymerization of an ethylene oxide-containing alkylene oxide and an organic compound containing two active hydrogen atoms, with a polycarboxylic acid, an anhydride thereof, a lower alkyl ester thereof, or a diisocyanate and is manufactured by spinning the same high molecular compound. The water-soluble fiber of the invention is not only high in elongation and tensile strength but is readily soluble in water.