Through a moderate ammonolysis method, nanobelts of α-MoO3 can be modified to HxMo(O, N)3. When reaction temperatures are kept between 200–300 °C, gaseous NH3 diffuses in-between the oxide layers and reacts with terminal oxygen sites of MoO3. As a consequence, hydrogen is introduced into the layers and bonded to terminal oxygen, and together with the effect of nitradation, the unit cell volume significantly shrinks mostly along the b axis. The modified compound HxMo(O, N)3 exhibits not only better electronic conductivity, but also faster lithium ion mobility than regular MoO3. In addition, this ammonolyzed MoO3 exhibits enhanced electrochemical performance beyond MoO3. In the potential window 1.5–3.5 V, the specific capacity of HxMo(O, N)3 can reach more than 250 A h kg−1 and was cycled 300 times without fading. It can be considered as a novel candidate cathode material with high specific charge for rechargeable Li-ion batteries.