A shoulder strap assembly and a snap hook structure thereof are presented. A strap of the shoulder strap assembly is combined with a first article through the snap hook structure. The snap hook structure includes a main body and a keeper member. The main body hooks the first article, and the keeper member ensures the main body to keep hooking the first article. The keeper member has a perforation. The user can wind the strap around a second article, and use a lock to pass through the perforation so as to lock the first article with the second article, thereby preventing the first article from being stolen.