This study aims to investigate flow and spray characteristics in twin-fluid atomization nozzles generating a supersonic annular gas jet, and the effect of shock wave interactions on liquid drops. Two different types of atomization nozzles were considered: sonic and converging-diverging nozzles. The annular gas jet behavior was identified by flow visualization and suction pressure measurements. Schlieren photographs shows that changes in atomizing gas pressure alter the net-shape wave patterns and the lengths of radially impinging stagnation point (recirculating toroid) and supersonic flow region. Suction pressures downstream of the nozzle orifice were measured to see the presence of shock cell and the influence of aspirating effect on atomization performance. Also examined were the fragmentation phenomena of liquid by still micro-photography using a spark light source. The drop size was measured by a light scattering method, and its radial distribution is obtained by use of a tomographical transformation. The atomization performances were compared for various atomizing conditions.