Abstract: An expansion screw includes an expansion sleeve having a conical plug assembled to an expandable front part thereof, a locating sleeve screwed to a rear part of the expansion sleeve, and a screw adapted to screw into the locating sleeve. The expansion sleeve includes an annular retaining groove between the expandable front part and the rear part thereof for receiving an O-ring therein. The O-ring is provided along its circumference with a plurality of claws that catch threads at the most front end of the screw to firmly hold the screw to the expansion sleeve. Therefore, the screw would not rotate and thereby loosen or separate from the locating and the expansion sleeves due to vibration caused by any external force, ensuring a secure and safe fastening of an item via the expansion screw.