In this paper, an Open-source code for Interfacial Energy Calculation (OpenIEC, https://github.com/openiec) was developed by following Kaptay's models (Acta Mater 60(19):6804-6813, 2012; J Mater Sci 53(5):3767-3784, 2018. 10.1007/s10853-017-1778-y). The coupling with the CALculation of PHAse Diagram thermodynamic and molar volume databases was facilitated in OpenIEC for providing the necessary thermodynamic information. With OpenIEC, the temperature- and composition-dependent interfacial energies in alloys with any arbitrary number of components can be conveniently evaluated. In order to demonstrate the applicability and validity of OpenIEC, the benchmark tests in several model alloys in Ni and Al alloys were carried out, and the calculated interfacial energies were found to be in good agreement with the literature data. After that, the OpenIEC was applied to predict the temperature- and composition-dependent interfacial energies of coherent /' interfaces in two Ni-based superalloys, including ternary Ni-Al-Cr and quaternary Ni-Al-Cr-Re alloys, as well as the temperature- and composition-dependent solid/liquid interfacial energies in Ni-Al-Cr and Al-Cu-Li alloys.