The electrochemical properties of nanocomposite SnO2–Se thin film prepared by pulsed laser deposition method have been investigated by cyclic voltammetry and charge/discharge measurements. A large reversible specific capacity of 958.8 mAh g−1 in SnO2–Se/Li cell cycled between 0.01 and 3.0 V is achieved. Our results have demonstrated that nanocomposite SnO2–Se exhibits larger capacity and better cycle performance than pure SnO2 and SnSe. The electrochemical reaction mechanisms of SnO2–Se with lithium are examined by X-ray diffraction, high resolution transmission electron microscopy, selected-area electron diffraction and spectroelectrochemical measurements. The reversible oxidation/reduction reaction of SnO2 and selenidation/reduction reaction of SnSe are revealed.