An OPJU file is a project created by Origin 2018 and later, a data analysis and graphing application used by various scientists and engineers. It contains all child windows in the project, which may include worksheets, 2D/3D graphs, and matrices. OPJU files also store project variables, imported filters, results log contents, and metadata.

OPJU file open in OriginLab Origin OPJU files replaced .OPJ files, which were the primary files used to save projects in all Origin versions before the 2018 version. OPJU files are saved in a unicode format which features performance advantages over the older OPJ file format. You can open OPJU files with Origin and Origin Viewer. Origin is the primary program used to create, open, and edit OPJU files but Origin Viewer is also commonly used since it is a free, lightweight program that allows you to view and copy information in OPJU projects in Windows and macOS. To open an OPJU file in Origin, select File → Open..., select the ".opju" file type, navigate to the OPJU file location, and click Open. To save an OPJU file in Origin, select File → Save project or Save Project As..., name the file, choose the save location, and click Save.