This paper focused on investigating the band alignment at the Cu2SnS3 (CTS)/In2S3 heterojunction interface by X-ray photoemission spectroscopy. An In2S3 over-layer was grown on a CTS thin film, which was grown by sulfurization of vacuum thermal evaporated Sn-Cu metallic precursors in a H2S:N-2 atmosphere. The valence band offset (VBO) at the CTS/In2S3 interface was measured to be 1.27 +/- 0.10 eV. The conduction band offset (CBO) was calculated from the measured VBO, giving (0.58 +/- 0.10) eV. These values show that the CBO has a spike-like behavior and the interface is a 'type I'. (C) 2015 Elsevier B.V. All rights reserved.