We have investigated the structural stability and energetics for small copper clusters, Cu-n (n=3,...,55) by using a Monte Carlo technique at room temperature (T=300 K). In the simulation we have adopted two approaches; one of them was optimizing the cluster from a random configuration as a starting point, and the other was optimizing the cluster by adding one atom randomly to an optimized geometry. The empirical potential-energy function proposed by Erkoc has been used, which contains two-body atomic interactions. It has been found that the fivefold symmetry appears in all the clusters with the number of atoms n greater than or equal to 7, and the icosahedral structure dominates in the clusters with the number of atoms n greater than or equal to 13. [S1050-2947(99)01810-7].