The variation of optical properties with the relative composition of AgGa1-xInxSe2 thin films prepared by the flash evaporation method (FEM) and the electron‐beam evaporation method (EBEM) has been investigated. Single‐crystalline films with (112) surfaces and polycrystalline thin films were grown, respectively, by FEM and EBEM with the former having the chalcopyrite structure. The energy gap for AgGa1-xInxSe2 thin films decreased with increasing X composition and a discontinuity near X=0.6 was observed for the crystalline thin films but not in the amorphous thin films. Also, the energy gap and the photoconductivity peak energy of these films decreased with increasing ambient temperature. The temperature coefficient of the energy gap is -(4–9)×10-6 eV/K (50–100 K) and -(2–7)×10-5 eV/K (100–300 K), and that of the photoconductivity peak energy is -(2.7–6.6)×10-5 eV/K (50–100 K) and -(4.3–7.8)×10-4 eV/K (100–300 K).