Abstract: A portable hard disk casing includes a hollow body with a front opening, a rear opening and two pairs of guiding tracks each formed on an inner face of the hollow body to be opposite to each other, two carriers for carrying thereon a storing unit, each carrier having two coupling ribs respectively formed on a side of the carrier to be opposite to one another to correspond to and to be received in the guiding tracks of the hollow body, a front cover to connect to the hollow body to cover the front opening of the hollow body and a rear cover to connect to the hollow body to cover the rear opening of the hollow body such that the storing unit is enclosed in the portable hard disk casing.