The Bookmarks tool in your Safari browser gives you a variety of options – you can add, remove, organize in groups, etc your bookmarks. Unfortunately, it lacks one very useful option – you cannot sort your bookmarks alphabetically.
There is, however, a workaround for this issue that still allows you to sort bookmarks in Safari alphabetically. First, drag the bookmarks folder to your Desktop. Switch to the Finder and open the folder. Choose the List view (View -> List) and then close the window. Once you have done that, you should drag the folder back to the Bookmarks window of Safari. If you browse to the newly added folder, you will note that it is sorted alphabetically now. The old, unsorted folder, however, will be still present in your Bookmarks window. Therefore, you can select it and press the delete key. You should delete the folder from the Finder too.
You should bear in mind that you can use this trick to sort your bookmarks only alphabetically. If you select any other sorting criteria in the Finder, your bookmarks will not be displayed in that order in Safari.