A two-dimensional layered Sb2Se3-based amorphous composite (a–Sb2Se3/C) is synthesized using a simple solid-state ball-milling process, and its potential for Li- and Na-ion batteries is evaluated. Ex situ extended X-ray absorption fine structure analyses clearly indicate the electrochemical reaction mechanisms of Sb2Se3 and a–Sb2Se3/C as anodes for Li- and Na-ion batteries. During Li- and Na-insertion, the Sb2Se3 and a–Sb2Se3/C electrodes are converted into the final phases of Li3Sb/Na3Sb and Li2Se/Na2Se, respectively. During Li- and Na-extraction, the Li3Sb/Na3Sb and Li2Se/Na2Se in the Sb2Se3 electrode are converted into Sb and Se, showing a non-recovery reaction, whereas a recovery to the original Sb2Se3 in the a–Sb2Se3/C electrode occurs after full Li and Na extraction. Owing to the interesting conversion/recovery reaction, the a–Sb2Se3/C electrode exhibits excellent electrochemical performance, such as high reversible capacities (Li-ion battery: 662 mAh g−1; Na-ion battery: 407 mAh g−1), a long cycle life with highly reversible capacities (Li-ion battery: 662 mAh g−1 and 1,205 mAh cm−3, respectively, after 100th cycle; Na-ion battery: 378 mAh g−1 and 688 mAh cm−3, respectively, after 50th cycle), and high rate capabilities (Li-ion battery: 623 mAh g−1 and 1,133 mAh cm−3 at 3C; Na-ion battery: 270 mAh g−1 and 492 mAh cm−3 at 2C).