Indium iodide (InI) is a compound semiconductor with a wide band gap. Due to its high atomic number (ZIn: 49 and ZI: 53) and high density (5.31 g/cm3), InI exhibits high photon stopping power similar to that of CdTe. Since InI has wide band gap energy (2.0 eV), radiation detectors fabricated from InI are expected to realize low-noise operation at and above room temperatures. Above-mentioned physical properties indicate that InI is a very promising material for fabrication of room temperature X- and gamma-ray detectors. In this study, radiation detectors were fabricated from InI crystals. InI materials were purified by the multi-pass zone-refining method up to 80 times. InI crystals were grown by the traveling molten zone method with the zone-purified materials. The resultant InI radiation detectors were evaluated by measuring their electrical property, spectral responses and long-term stability. The resistivity of the InI detectors were found to be approximately 3 × 109 (Ωcm). The InI detector exhibited a clear peak corresponding to 22 keV X-rays from a 109Cd radioactive source at room temperature. In order to evaluate the long-term stability of the InI detectors, temporal change of the energy spectra of the detectors was measured for a period of time at 20°C and at -20° C. At 20°C, the InI detectors exhibited the degradation in spectral response. On the other hand, the InI detectors operated stably for more than 32 hours at -20°C.