A computer-implemented method for applying data loss prevention policies to closed-storage portable devices may include (1) injecting a data loss prevention component into at least one application process that is running on a computing device, (2) intercepting, via the data loss prevention component, an attempt by the application process to transfer a file to a closed-storage portable device that is connected to the computing device, (3) identifying a data loss prevention policy that applies to the attempt by the application process to transfer the file, (4) determining that the attempt by the application process to transfer the file violates the data loss prevention policy, and (5) performing a security action in response to determining that the attempt by the application process to transfer the file violates the data loss prevention policy. Various other methods, systems, and computer-readable media are also disclosed.