Abstract: The morphological structure, dimensions and mechanical properties of fiber bundle in cotton stalk epidermis and xylem were investigated using optical microscope and fiber tensile strength tester after they were disposed by rub silk process. The length, width, the radio and the crosssectional areain cotton stalk epidermis were 2512 mm, 2019 μm, 15878, and 42 11969 μm2, respectively. The length, the width, the radio, and the crosssectional areain cotton stalk xylem were 1357 mm, 25336 μm, 7688, and 69 24616 μm2, respectively. The length and radio of the fiber bundle in cotton stalk epidermis were lower than that in the xylem. The width and rosssectional area in cotton stalk epidermis were higher than the area in the xylem. The tensile stress, elastic modulus and elongation of fiber bundle in epidermis were 6073 MPa, 217 GPa, and 43, and those in the xylem were 4258 MPa, 133 GPa, and 311, respectively. Fiber bundle in epidermis has a better flexibility because the tensile stress, elastic modulus and elongation in cotton stalk epidermis were higher than those in the xylem. The mechanical property of cotton stalk was poorer, compared with other plant fibers. The mechanical property of fiber bundle in epidemic was lower than single cotton stalk fiber. The results provided the essential data for cotton stalk fiber used in plant fiber composites as the reinforced materials.