The mechanically exfoliated ultrathin 3R α-In2Se3 nanosheets were transferred onto a SiO2/Si substrate. Using atomic force microscopy, it was confirmed that the transferred α-In2Se3 transferred had a thickness of 15–120 nm. The thickness-dependence of Raman peaks of E2A11E4A12λ, E2A11E4A12λ, E2A11E4A12λ, and E2A11E4A12λ was observed from the Raman spectra. Moreover, the measured photoluminescence peak values in the range of 869–895 nm indicate a blue shift as the thickness decreases. The field-effect transistor based on α-In2Se3 exhibited an n-type semiconductor behavior. From the transfer curve at gate voltage of 10 V, the derived values of the mobility and ON/OFF ratio are 24.26 cm2 V− 1 s− 1 and 1.84, respectively. In addition, it was confirmed that the 3R α-In2Se3 layers had a high photoresponsivity of up to approximately 34,500 A/W under illumination (E2A11E4A12λ = 750 nm).Graphical abstract: