A side lock sleeve assembly includes: a first tube, a sleeve having a first coupling portion defining a first receiving space for sleeving over the first tube, wherein a hole is formed on the first coupling portion at a position between a center of the first receiving space and an outer surface of the sleeve; and a fastening screw having an operation section and an extension section, wherein a diameter of the screw gradually decreases from the operation section toward the extension section such that threadedly extension of the extension section through the hole to retain the extension section between the sleeve and the first tube and such that threadedly insertion of the extension section of the screw through the hole results in a threaded fitting portion on an outer surface of the first tube complementing with the extension section, thereby snugly receiving the extension section of the screw therein.