Compounds of the chalcogenide family Ag-In-VI (VI=S, Se, Te) are interesting materials because of their stoichiometric stability and potential application in non-linear optics and solar cells. For this work, an ingot of AgIn5Se8, an ordered vacancy compound, was prepared by direct fusion of the stoichiometric mixture of the elements in an evacuated quartz ampoule. The analysis of the X-ray powder diffraction data showed the presence of a single phase with tetragonal structure at room temperature. The lattice parameters a and c were calculated, giving 5.795224 Å and 11.627038 Å, respectively. Differential ThermalAnalysis measurements were performed on samples in evacuated quartz ampoules. A solidÂsolid (order-disorder) transition was observed at 730 ºC, while the melting temperature was found to be 810 ºC. Transmittance and reflectivity measurements were used to calculate the absorption coefficient from which two energy gaps were estimated, 1.24 eVand 1.46 eV, indirect and direct, respectively.Alternatively, from the fit of the reflectivity, the indirect energy gap and the direct energy gap turned out to be 1.28 eV and 1.48 eV, respectively. The real refraction index, also obtained fromthe fit of the reflectivity, resulted to be 4.05.