In this paper, an analytical technique for calculating the amplitude of reflected sound waves from a rigid rectangular body with curved surface is described. This theory is based on the assumption that a receiver is located independently from a transmitter. The formulas for the reflctivity are derived approximately under certain restrictions of geometrical optics. The reflectivity, which is termed "directional sound reflectivity", is defined as the ratio of the reflected sound pressure from a target to the calculated one which is derived the theory of geometrical optics. To verify the validity of the approach, some experiments were performed in air at the frequency of 39. 80kHz. Experimental results showed good agreement between the calculated and the measured values and this confirmed the usefulness of the present technique to calculate the reflection of sound waves from a rigid rectangular body with curved surface.