Spinel Li4Ti5O12 known as a “zero-strain” anode material for Li-ion battery has attracted much attention because of its superior safety and stability. Herein, we report a novel H2O2-assisted one-step hydrothermal method to synthesize different ratio Li4Ti5O12/TiO2 composites with the same amount of raw materials. For the first time, Li4Ti5O12 was prepared directly from commercial titania with the presence of H2O2, and different proportion Li4Ti5O12/TiO2 composites were fabricated only by adjusting the amount of H2O2. The reaction mechanism of the novel H2O2-assisted method was clearly investigated, and H2O2 plays a crucial role in the formation of intermediate Li1.81H0.19Ti2O5·2H2O. Further, the electrochemical performance of different ratio Li4Ti5O12/TiO2 composites have been investigated. This facile method is also applicable for the preparation of Na2Ti6O13/TiO2 material, and provides us the new way to fabricate composite materials.