Silicon monoxide (SiO) is utilized as an anode material in Li-ion batteries. The electrochemical properties of the SiO anodes are investigated. The SiO exhibits a high initial capacity of ∼2083 mAh g<sup>−1</sup>, while it has poor cycling stability. Thermal properties of SiO electrodes in mixing with or without the electrolyte are investigated by using DSC for the first time. Both lithiated and delithiated SiO electrodes show exothermic peaks in DSC curves, presumably due to the decomposition of electrodes. By changing the ratio between the cycled electrodes to the electrolytes, thermal behavior of the mixtures is studied in detail. The dominant exothermic peak at around 290°C is attributed to the reactions between lithiated electrode and electrolyte after the thermal breakdown of the SEI. Li in the electrodes and electrolytes should be responsible for the thermal risk in application of SiO batteries. The heat value of SiO based on capacity is estimated to be 1.85 J mAh<sup>−1</sup>, which is much smaller than that of graphite (5.11 J mAh<sup>−1</sup>). Hence, the SiO can be thermally safer than graphite.