To obtain an intermediate natural textile product having effective long-term antimicrobial characteristics according to an add-on treatment by applying an effective amount of an antimicrobial agent by an open type wet processing.

A natural fiber such as cotton fiber is filled in a treating basket, then placed in a kier, treated with an aqueous solution of caustic soda, washed, neutralized with an acid, subsequently bleached with hydrogen peroxide and treated in an aqueous solution capable of applying (hexamethyenediguanido) hydrocloride or diiodomethyl p-tolyl sulfone in an amount of 1.0% or 0.4% based on the fiber weight, then taken out of the kier and dried to afford the cotton fiber to which an effective amount of the antimicrobial agent is cationically bonded to the cotton fiber.