Si nanospheres (SiNSs) have been synthesized via a simple, continuous and one-step way by using a radio frequency (RF) thermal plasma system on a large-scale. The synthesized SiNSs display a perfect spherical shape with a smooth surface and good dispersity. By a simple ball-milling post-processing, silicon nanosphere/porous carbon (SiNS/PC) composites with synthesized Si nanospheres uniformly dispersed in the carbon matrix have been prepared, and the composite particles have a core/shell structure (i.e., every Si nanosphere is well covered by the complete porous carbon shell). As anodes for Li-ion batteries, the prepared composite materials could maintain microstructural stability after cycles and exhibit remarkably improved electrochemical performance with large storage capacity, super cycling stability and high rate capability. These desirable electrochemical performances are attributed to the unique structure of the SiNS/PC composite, which has a high capacity Si core with a nanosphere morphology to alleviate the inner volume changes, and a porous shell acting as a conductive matrix to enhance the conductivity, accommodate the silicon volume expansion, and facilitate lithium-ion transportation during charging-discharging.