Germanium oxide (GeO2) films with two different grain sizes of 10nm (GeO2 (10nm)) and 100nm (GeO2 (100nm)) were grown via reactive radio frequency sputtering at different temperatures. Electrochemical measurements of the GeO2 (10nm) thin film used as an anode in Li ion rechargeable batteries show superior capacity retention and rate capability compared to those of GeO2 (100nm). The GeO2 (10nm) thin film possesses an initial capacity of 930mAhg−1 with 89% capacity retention after 100 cycles, compared with 455mAhg−1 with 53% of GeO2 (100nm) and 225mAhg−1, 30% (10 cycles) of common macro-size GeO2. Microstructural studies reveal that the GeO2 (10nm) thin film can better accommodate volume changes during Li–Ge alloying and de-alloying processes.