Formation and shape of the gold islands formed by vacuum deposition on the highly oriented pyrolytic graphite (HOPG) surface has been studied by means of scanning tunneling microscopy (STM). In the early stage of formation, gold atoms tend to aggregate into large clusters, which may be disturbed easily by the STM tip in the course of imaging. With the increasing coverage, the gold clusters can move and coalesce into large oblong islands, and the islands can further aggregate into clusters with variable shapes. When the coverage reaches about 20 monolayers, the islands or island clusters can be imaged without being disturbed by the tip, provided that the tunneling resistance is high enough. It has been noticed that the islands have a very similar ratio of width to height. The value of this ratio indicates that the islands essentially have a thermodynamically equilibrium shape. Such islands formed by self assembly may have potential in investigations of mesoscopic physics as well as applications.