Abstract: In order to improve the aldehyde production quantity of oxidized cotton fibers,the pretreatment of cotton fibers with sodium hydroxide was performed before selective oxidation in this paper.The structure and properties of selective oxidized cotton fibers before and after alkali pretreatment are compared.The results show that after alkali pretreatment,the chemical structure of the cotton fibers has little change.While the cellulose crystal has been transformed from cellulose I to II structure and the crystallinity has been decreased constantly with increasing alkali concentration to 25%,which has greatly improved the accessibility and the reactivity of the cotton fibers.FT-IR study shows that the intensity of the aldehyde absorption peak for the oxidized cotton fibers after alkali pretreatment exhibits stronger than that before pretreatment.Under(8 g/L) and(32 g/L) NaIO_4 conditions,increasing alkali concentration enhances the aldehyde group content of the oxidized cotton fibers and decreases gradually the crystallinity of the samples.However,at higher concentration of alkali and oxidant,the increment of the aldehyde content and the degradation degree of cotton fibers slows down during the oxidation process.