The development of magnesium ion batteries as a viable alternative to lithium-ion batteries is impeded by the lack of efficient and stable electrode materials. Here, we present the synthesis of nanocomposites of tin-containing silicon oxycarbonitride (Sn/SiOCN) as anode materials for magnesium ion batteries (MIBs). The elemental and phase composition, morphology, and surface area of the nanocomposites are assessed by several characterization techniques. The galvanostatic cycling tests indicate a substantial initial discharging capacity for the anode with 42.2 wt.% of tin. Specifically, the first discharging capacities are 489.9 mA/g, 172.9 mA/g, and 136.6 mA/g at current densities of 0.5 mA/g, 50 mA/g, and 500 mA/g, respectively. After 100 cycles at a current density of 500 mA/g, the anode containing 33.8 wt% of tin exhibits a reversible capacity of 101.8 mAh/g and a remarkable rate performance efficiency of 76.5%. Increasing tin content in the electrode materials increases the battery performance by decreasing electrode impedance and thus facilitating Mg2+ diffusion, as revealed by electrochemical impedance spectroscopy (EIS). Ex situ XRD and X-ray photoelectron spectroscopy (XPS) characterizations following the magnesiation-demagnesiation process confirm the storage of reversible storage of Mg2+ ions in Sn/SiOCN electrode through incorporation in the SiOCN network and alloying/dealloying process involving Mg-Mg2Sn-Mg.