PURPOSE: To accomplish easily in high yield the collection of the high-purity title fiber as a feedstock for paper through utilizing wastes by treating the stems of corn, soybeans and/or potatoes with a specific solution to collect bast and repeating the above treatment.

CONSTITUTION: The stems of corn, soybeans and/or potatoes is put, at normal temperatures to 80°C, into a solution containing 0.02-0.3mol of sodium hydroxide and 0.01-0.2mol of hydrogen peroxide and treated to remove bast therefrom. Thence, said bast thus collected is put, where needed, to physical treatment such as crushing with a roller to obtain crude fiber, which is then further put, at 55-80°C, into a solution containing 0.05-2mol of sodium hydroxide and 0.0-0.3mol of hydrogen peroxide and treated, thus collecting the objective fiber.