In this paper, we report on the preparation of Sn (core)–Al (shell) nanocomposite thin films by co-sputtering Sn target and Al target, and their application as anode of lithium-ion batteries. Instrumental analyses of X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscope have been used to characterize the structure and morphology. The results reveal that the thin film is composed of core–shell structure with Sn nanoparticle core and Al amorphous shell. Furthermore, measurements of charge–discharge, cyclic voltammetry and electrochemical impedance spectroscopy have been employed to characterize the electrochemical performance of Sn–Al film. The Sn–Al thin film with 18wt% Al delivers high capacities of 822, 460 and 313mAhg−1 in the second 2nd, 60th and 200th cycles, respectively. Meanwhile, a discharge capacity of 420mAhg−1 is obtained at 3000mAg−1. The excellent electrochemistry performance is owing to the core–shell structure in which Al shell can alleviate the expansion of volume of Sn particles and restrain the aggregation of Sn particles. The results indicate that Sn–Al thin film is a promising anode for lithium-ion batteries.