A modular fire safe is provided. The modular fire safe includes a base module. The base module has an interior shell and one or more groove assemblies. One or more intermediate modules are positioned in a vertically stacked arrangement with the base module. The one or more intermediate modules have an interior shell, one or more groove assemblies and one or more tongue assemblies. A top module is positioned in a vertically stacked arrangement with an uppermost intermediate module. The top module has an interior shell and one or more tongue assemblies. The tongue assemblies are configured to be received by the groove assemblies such that the base, intermediate and top modules form an assembled modular fire safe. A plurality of retention members extend transversely through the interior shells of the base, intermediate and top modules to secure the tongue assemblies to the groove assemblies.