PURPOSE: To obtain the titled fiber useful for making toilet paper, etc., comprising water-insoluble hydrogel, losing gradually bonding strength in a wet state, by subjecting aqueous dope containing an alginate and an alginic acid alkylene glycol ester to wet spinning.

CONSTITUTION: A mixture of an alginate (e.g., alginate acid etc.,) and an alginic acid alkylene glycol ester (e.g., aliginic acid propylene glycol ester, etc.,) in a weight ratio of usually 95:5W10:90 is dissolved in water in a concentration of usually 2W10wt% to give aqueous dope. The dope is then spun, for example, introduced into a coagulating bath containing a water-soluble salt (calcium chloride, etc.,) of a metallic ion which can be replaced with a cation of the water-soluble alginate and insolubilized. The prepared yarn is taken-up, cut into preferably 2.0W10.0mm length and dried to give the aimed yarn.