A portable door lock is provided for a door having a latch engageable in an aperture in a latch plate secured to a door frame, the latch plate having a tongue extending into the aperture from a front edge of the latch plate, and the tongue being spaced from the top and bottom of the aperture. The door lock includes a retainer positionable against the latch plate to permit closing of the door and having a pair of vertically spaced fingers insertable into the latch plate aperture to engage the front edge thereof above and below the latch plate tongue. A retainer shaft extends forwardly from the retainer and has a screw-thread portion, and a holding bracket has a medial portion slidably mounted on the shaft and rearwardly projecting holding arms at opposite ends. A holding nut threadingly engages the screw-threaded portion of the retainer shaft to hold the bracket arms against the door frame and the door respectively, when the door is closed and the retainer is engaged with the latch plate, to prevent the door from being opened.