High-capacity Li2MnSiO4/C (LMS/C MBS) nanoparticles have been prepared using sonochemistry under a multibubble sonoluminescence (MBS) condition, and their physical and electrochemical properties were characterized. The results show that LMS/C MBS nanoparticles exhibit a nearly pure crystalline phase with orthorhombic structure and have a spherical shape and a uniform particle size distribution centered at a diameter of 22.5 nm. Galvanostatic charge–discharge measurements reveal that LMS/C MBS delivers an initial discharge capacity of about 260 mA h g−1 at a current rate of 16.5 mA g−1 in the voltage range of 1.5–4.8 V (vs. Li/Li+), while LMS MBS (LMS without a carbon source under MBS) and LMS/C SG (LMS with a carbon source using the conventional sol–gel method) possess lower capacities of 168 and 9 mA h g−1, respectively. The improved electrochemical performance of LMS/C MBS can be ascribed to the uniform nanoparticle size, mesoporous structure, and in-situ carbon coating, which can enhance the electronic conductivity as well as the lithium ion diffusion coefficient.