Abstract: Fibers with lignin content of 4.5% and fineness of 28.3 dtex were extracted from bark of cotton stalks using 4% alkali at 160℃ for spinning application. Bark of cotton stalks, with cellulose content of 40%, is a copious and inexpensive source for natural fibers. However, cotton stalk fibers extracted using conventional method, such as alkali, steam explosion or H2O2, had too coarse fineness (>45 dtex) or too high lignin content (>11.8%), which rendered them to be made into high quality yarns. In this research, bark of cotton stalks was treated by 4% alkali at temperature of 150, 160 and 170℃, respectively. Time of alkali treatment was regulated to achieve fibers with good fineness and proper breaking strength for spinning application. Effects of alkali conditions on the dimension, composition, tensile property and crystalline structure of cotton stalk fibers were investigated. The results showed that fineness of cotton stalk fibers decreased gradually with the increase of time. However, excessively long time would cause drastic decrease in fiber length and bark of cotton stalks was even completely disintegrated into paste. Fibers extracted at temperature of 150, 160 and 170℃ had the best fineness of 30.8, 28.3 and 28.1 dtex, respectively. Increasing time reduced the lignin content of cotton stalk fibers. Fibers extracted at temperature of 150, 160 and 170℃ had the lowest lignin content of 5.1%, 4.5% and 4.5%, respectively. Moreover, the increase in the time and temperature also caused a drastic decrease in breaking strength and Young's modulus. Fibers extracted at temperature 160℃ had breaking strength of 1.8 cN/dtex whereas breaking strength of fibers extracted at temperature 170℃ decreased to only 1.4 cN/dtex. Therefore, fibers extracted by 4% alkali at 160℃ with time of 60 min had the best properties, including fineness of 28.3 dtex, length of 39 mm, lignin content of 4.5% and Young's modulus of 46 cN/dtex. All fibers in this research had crystalline structure of type I, indicating that alkali treatment did not change the crystalline structure of cellulose in cotton stalk fibers. Compared to the best cotton stalk fibers in references, fibers in this research had similar fineness but lower Young's modulus, which was due to more thorough removal of lignin at temperature of 160℃. Cotton stalk fibers with lignin content of 4.5% and 5.5% could be spun into yarns with fineness of 22.4 tex. When lignin content of cotton stalk fibers was decreased from 5.5% to 4.5%, unevenness and hairiness index of blended yarns were lowered by 75.1% and 29.6%, respectively, but breaking strength and breaking elongation increased by 11.1% and 9.8%, respectively. Scanning electron microscope (SEM) images of blended yarns also showed that fibers with lower lignin content could be spun into yarns with better structure. Fineness of yarns in this research was 68% lower but breaking strength was 93.5% higher than that in references, respectively. Overall, cotton stalk fibers extracted at 160℃ are characterized with low lignin content and low Young's modulus, which endow them a good potential to be used for making high quality yarns.