Nanostructured SnO2/C microfibers were prepared by thermal decomposition of tin alginate fibers produced via wet-spinning technique. Results of X-ray diffraction and scanning electron microscopy show that the as-obtained SnO2/C microfibers consist of nano-sized SnO2 crystals with a mean diameter of 10-15 nm. Transmission electron microscopy visualization reveals that the composite fibers exhibit a porous structure consisting of both micropores and mesopores. Electrochemical evaluations of cyclic voltammetry and galvanostatic charge-discharge indicate that the SnO2/C microfibers possess a high capacity and good rate capability compared with commercial SnO2. The improved performances of SnO2/C fibers can be attributed to the nano-size of SnO2 particles dispersed in carbon matrix and the existing nanopores in the SnO2/C microfibers.