An analytical method was developed to study the wave diffraction effects on arc-shaped bottom-mounted breakwaters. The breakwater was assumed to be rigid, thin, impermeable and vertically located in water of constant depth. The fluid domain was divided into two regions by imaginary cylindrical interface. The velocity potential in each region was expanded with eigenfunctions. By satisfying continuity of pressure and normal velocity across the imaginary fluid interface, a set of linear algebraic equations could be obtained to determine the unknown coefficients for eigenfunction expansions. The accuracy of the present model was verified by a comparison with existing results for the case of an isolated straight-line breakwater. Numerical results, in the form of contour maps of the non-dimensional wave amplitude around the breakwater and diffracted wave amplitude at three typical sections, were presented for a range of wave parameters. Results show the arc-shaped bottom-mounted breakwater is generally effective in defending against waves. The wave amplitudes at most sheltered areas are commonly 10%-50% of incident wave amplitudes under most wave conditions.