We use confocal μ-Raman spectroscopy to characterize the local microstructure of SiOx particles that are composed of amorphous and crystalline phase and to understand its effects on electrochemical reactions. Particles of bare SiOx (x∼1) consist of an inhomogeneous mixture of a-Si and c-Si; some particles mainly have a-Si phase but others consist mainly of micro-sized crystalline Si phase. In contrast, particles of C-coated SiOx are composed of uniform nano-sized crystalline Si embedded in a-SiO2 matrix with small amounts of a-Si. The two samples had different electrochemical properties due to this difference in microstructure. Initial coulombic efficiency (ICE) and capacity retention were higher in the C-coated SiOx than in the bare SiOx. The findings demonstrate that confocal μ-Raman spectroscopy is very useful tool for characterizing the microstructure of SiOx and the understanding of local microstructures of SiOx is very important for understanding electrochemical reactions.