A method and apparatus for reserving a usable storage space on a storage device is provided. The method includes collecting context data representing an environment surrounding the storage device; selecting at least one file from among files stored in the storage device by using at least one of the context data and user profile data; and processing the selected file and reserving a usable storage space on the storage device. The method reserves the usable storage space by using the context data or user profile data, thereby allowing efficient reserving of usable storage space without a user's manual intervention and preventing waste of unnecessary resources.