The present invention is a portable multi-purpose universal serial bus (USB) structure, which refers to a storage unit that can be provided inside a casing and has a USB connector exposed out of one end of the casing. The casing can be a casing for a key, a vehicle anti-theft alarm, a controller of an electric roller gate, or a receiver of an entrance guard card, thereby avoiding the user from forgetting to carry said objects when going out and therefore from incurring any inconvenience.