SUMMARY: BioModTool is a Python program allowing easy generation of biomass objective functions for genome-scale metabolic models from user data. BioModTool loads biomass composition data in the form of a structured Excel file completed by the user, normalizes these data into model-compatible units (mmol.gDW AVAILABILITY AND IMPLEMENTATION: BioModTool is publicly available on PyPI (https://pypi.org/project/BioModTool/) under a GNU Lesser General Public License (LGPL). Installation instructions and source code are available on GitHub (https://github.com/Total-RD/BioModTool). BioModTool is compatible with Windows, Linux, and MacOS operating systems.