A facile microwave hydrothermal route is employed to synthesized NH4V3O8 ultralong nanobelts without any surfactant. The prepared NH4V3O8 nanobelts have an average width of 40–60nm and a length of tens of micrometers growing along [001] direction. When used as cathode material for lithium ion battery, the NH4V3O8 nanobelts show high discharge capacity (337mAhg−1 at 15mAg−1), nice cycling stability (98% after 100 cycles) and good rate capability (279, 248, 220, and 192mAhg−1 at 60, 120, 240 and 300mAg−1, respectively). The good electrochemical property of the NH4V3O8 is attributed to its unique ultralong nanobelt structure with good structural stability.