Sm-doped Li₄Ti₅O₁₂ (LTO) in the form of Li_4−x/3Ti_5−2x/3Sm_xO₁₂ (x = 0, 0.01, 0.03, 0.05 and 0.10) is synthesized successfully by a simple solid-state reaction in air. XRD analysis and Rietveld refinement demonstrate that traces of the doped Sm³⁺ ions have successfully entered the lattice structure of the bulk LTO and the Sm doping does not change the spinel structure of LTO. However, of interest is that the lattice parameter increases gradually with the increase of the Sm doping amount, which is potentially beneficial for intercalation and de-intercalation of lithium ions. XPS results further identify the existence of Ti³⁺ ions and the transition of a small quantity of Ti ions from Ti⁴⁺ to Ti³⁺, which will improve the conductivity of LTO. All materials are well crystallized with a uniform and narrow size distribution in the range of 0.5–1.2 μm. The results of electrochemical measurement reveal that the Sm doping can improve the rate capability and cycling stability of LTO. Among all samples, Li_4−x/3Ti_5−2x/3Sm_xO₁₂ (x = 0.03) exhibits the best electrochemical properties. The specific capacities of the Li_4−x/3Ti_5−2x/3Sm_xO₁₂ (x = 0.03) sample at charge and discharge rates of 5C and 10C are 131.1 mA h g⁻¹ and 119.2 mA h g⁻¹, respectively, compared with 64 mA h g⁻¹ (5C) and 47 mA h g⁻¹ (10C) for the pristine LTO in the potential range 1.0–2.5 V (vs. Li/Li⁺). This result can be attributed to Li_4−x/3Ti_5−2x/3Sm_xO₁₂ (x = 0.03) with a diffusion coefficient of 1.3 × 10⁻¹² cm² s⁻¹, which is higher than the 7.4 × 10⁻¹⁴ cm² s⁻¹ for the LTO electrode without Sm doping. In the meantime, the discharge capacity of Li_4−x/3Ti_5−2x/3Sm_xO₁₂ (x = 0.03) can still reach 125.1 mA h g⁻¹ even after 100 cycles and maintain 95.2% of its initial discharge capacity at 5C. Therefore, Sm doping has a great impact on discharge capacity, rate capability and cycling performance of LTO anode materials for lithium-ion batteries.