NH4V3O8 with belt-like morphology has been synthesized via a hydrothermal process, using acetic acid as acidulant. The resulting phase-pure NH4V3O8 microcrystals have smooth surfaces and are typically 25–45μm long, 2–15μm wide, and 0.6–1.2μm thick. Electrochemical studies by means of cyclic voltammetry and galvanostatic cycling show that the pristine material is a suitable host for reversible Li+ de-/intercalation. Analysis of the peak currents from cyclic voltammetry by means of the Randles-Sevcik equation suggests that the Li+ de-/intercalation is diffusion-controlled with D ∼5·10−15 cm2 s−1. The maximum discharge capacity, at 20mAg−1, amounts to 299mAhg−1. At 90mAg−1, it is still 201mAhg−1 with a capacity retention of 90% in the 100th cycle, indicating the belt-like NH4V3O8 being a promising candidate for application as cathode material in secondary lithium-ion batteries.