A method for producing crystalline sulphated cellulose II materials with relatively low degree of polymerization from spent liquors of sulphuric acid (H2SO4) hydrolysis of cellulose has been discovered. The method involves: 1) separating the spent liquors from the hydrolysed, acid-insoluble, cellulose I materials by dilution from, for example, a 64% H2SO4 hydrolysis medium to a residual sulphuric acid concentration of 10-50% with 0-40% H2SO4, followed by settling (or centrifuging) and decanting； 2) adding the diluted spent liquors to water or heating the diluted spent liquors at 30-80° C. for &nlE；48 h； and 3) recovering the recrystallized sulphated cellulose II materials with relatively low degree of polymerization either by filtration and washing or by washing and freeze drying. The method can be used to concurrently produce both crystalline, sulphated cellulose I and the crystalline, sulphated cellulose II materials.
