In this paper, the bast of the Kosteletzkya virginica are degummed and separated into fine fibers, the chemical composition, morphology, microstructure and mechanical properties of the Kosteletzkya virginica bast fibers are characterized by means of SEM, ART-FTIR, DSC-TGA, XRD and Instron tensile tester. The results show that the surface of the Kosteletzkya virginica bast fibers is smooth, and there are many visible grooves along the vertical section. Typical cellulose I in the Kosteletzkya virginica bast fibers is confirmed by FTIR and XRD analysis. The crystallinity of the Kosteletzkya virginica bast fibers is higher than that of the cotton fibers and lower than that of the castor-oil plant bast fibers. The beginning and maximum decomposition temperature of the Kosteletzkya virginica bast fibers are 252 and $347^{circ}C$ respectively, which indicate that the Kosteletzkya virginica bast fibers have an appropriate thermal stability. The Kosteletzkya virginica bast fibers have a better mechanical properties and excellent hygroscopicity. All the results show that the Kosteletzkya virginica bast fiber is one of an ideal candidate for the new textile material.