To provide a method for separating a vegetable fiber, capable of saving energy and being environmentally friendly in order to solve problems in which a conventional separation means for separating a plant body into cellulose and lignin consumes energy in large amounts and is dangerous and severe to the environment, because the plant body is boiled in 25-30% alkali solution at about pH 14 for several hours in the conventional means.

A plant body is ground by a means (e.g. a grinder or a mortar) for making the particle diameter small and sorted by a sorting means such as a sieve to provide plant body powder sorted into ≤0.5mm particle diameter and the plant powder is mixed with an aqueous solution of an alkali and then, a solid component is separated from a liquid component and the solid component is washed with water to provide the vegetable fiber.