The Sn/C nanocomposites are of great interest as high capacity anode materials for lithium ion batteries (LIBs). In this paper, we employ a tandem plasma reaction method for controlled preparation of Sn/C binary composites. The Sn and C components are generated by magnetron sputtering and plasma decomposition of CH4 in two tandem plasma zones, respectively. The obtained Sn/C composites are composed of ultrafine Sn particles homogeneously embedded in carbon matrix, which exhibit very high reversible lithium storage capacity. The tandem plasma reaction method offers great versatility in controlling the Sn/C ratio and the Sn particle size, allowing a systematic study on the relationship between the structural parameters and the electrode performance. The reversible anode capacity is found to be strongly affected by the Sn particle size while it shows a much weaker correlation with the carbon coating layer.