Cobalt oxide fibres are synthesised via electro-spinning followed by calcination in air at 600 degrees C. Texture, morphology and surface composition of the fibres, as well as phase of the oxide formed are investigated by means of a combination of characterisation techniques. The electrochemical performance of the electro-spun Co3O4 fibres as anode material in Na-ion rechargeable batteries is evaluated, and the conversion reaction mechanism is investigated by carrying out ex-situ analyses on the cycled electrodes. The formation of the CoO after the first sodiation/desodiation cycle accounts for the cathodic specific capacity lowering from 983 down to 580 mAh g(-1). The high aspect ratio morphology of the fibres is responsible for the high value of initial cathodic specific capacity and the slow capacity fading (after 30 cycles, a cathodic capacity of 407 mAh g(-1) is retained).