The present invention discloses UV-epoxy and ultrasonic case assembly methods for a USB flash drive, wherein a transparent or translucent top cover is fastened to a bottom cover containing a printed circuit board assembly via an UV-cure epoxy glue or an ultrasonic weld method. As the top cover of the USB flash drive is transparent or translucent, the USB flash drive has a see-through property and presents an aesthetic taste, which can attract the attention of consumers. Further, the method of the present invention uses less case parts and fewer steps and thus can fabricate a USB flash drive having a lower cost and a better quality at a higher throughput. Furthermore, the USB flash drive fabricated according to the method of the present invention has a better moisture resistance and a better water resistance.