Presented are the STM images of self-assembled monolayer of 2-mercaptoethanol on Au(111). Striped structures of ($6{ imes}3_{frac{1}{2}}$), ($5{ imes}3_{frac{1}{2}}$), ($4{ imes}3_{frac{1}{2}}$) and compact-($5{ imes}3_{frac{1}{2}}$) were observed after annealing at $80^{circ}C.$ Analysis of the ordered structures revealed that the basic fundamental units of the ordered structures were three crystallographically non-equivalent ($3_{frac{1}{2}}{ imes}3_{frac{1}{2}}$) $R30^{circ}$ assemblies, and that the way of combination of the assemblies produced the four different structures. The($6{ imes}3_{frac{1}{2}}$) structure ( $ heta$ = 0.33) was composed of one ($3_{frac{1}{2}}{ imes}3_{frac{1}{2}}$)$R30^{circ}$ assembly, while the ($5{ imes}3_{frac{1}{2}}$) ( $ heta$ = 0.30) and ($4{ imes}3_{frac{1}{2}}$) ( $ heta$ = 0.38) structures were consisted of two ($3_{frac{1}{2}}{ imes}3_{frac{1}{2}}$) $R30^{circ}$ assemblies, separated by 5a and 4a, respectively. Furthermore, the compact-(5X 3½) structure ( $ heta$ = 0.50) was obtained by overlapping three ($3_{frac{1}{2}}{ imes}3_{frac{1}{2}}$) $R30^{circ}$ assemblies. In spite of the diversity in the adsorption structures, all the adsorption sites of 2-mercaptoethanol were fundamentally identical. On the other hand, the unannealed primitive SAM of 2-mercaptoethanol was characterized by two observations: a short-range order keeping the adsorbed molecules at approximately $3_{frac{1}{2}}$ a and the small domains of the striped structures supporting that the observed surface structures on the annealed surface were the extension of the primitive layer of 2-mercaptoethanol. Comparing these observations with the already published structures of ethanthiol, it was concluded that the interaction between the hydroxyl groups of 2-mercaptoethanol might play a significant role in the adsorption step of 2-mercaptoethanol on Au(111) to organize the adsorption structures different from those of ethanthiol.