To clarify the reaction mechanism of SiO anode, the chemical and the electrochemical reactions of SiO and SiO<sub>2</sub> with Li-metal and first principles calculations were investigated. In the chemical reactions, SiO and amorphous SiO<sub>2</sub> formed lithium silicide (Li<sub>44</sub>Si<sub>5</sub>) and lithium silicate (Li<sub>2</sub>SiO<sub>3</sub>, Li<sub>4</sub>SiO<sub>4</sub>) by reacting with Li. In the electrochemical reactions, crystalline SiO<sub>2</sub> did not react with Li though amorphous SiO<sub>2</sub> did do so. These results indicated that both Si area and amorphous SiO<sub>2</sub> area in SiO matrix play an important part in SiO charge–discharge process. This suggests that the dangling-bond in amorphous SiO<sub>2</sub> can react with Li easily. This finding was also confirmed by first principles calculations using VASP code.