The electrochemical performance of CoO-filled multi-walled carbon nanotubes (MWCNTs) is described. WCNTs were purified, opened and filled with cobalt salt in one-step by wet-chemistry-route. Followed by calci-nations in Ar atmosphere, the salt filled in the MWCNTs decomposed to CoO subsequently. Structural characteri-zation of the composite material by X-ray diffraction and transmission electron microscopy showed that MWCNTs were filled by discrete nano-size CoO. Compared to the MWCNTs purified by HNO3, the CoO-filled MWCNTs ex-hibited higher capacity-and better cyclability during galvanastatic charge-discharge cycling and cyclic voltamme-try (CV) tests.