This paper reports on an experimental study of dispersion process of an air-assisted injected spray with a view of optimizing its characteristics. A phase Doppler anemometer was used to measure the injected spray characteristics under open air condition. Ensembled average mean diameters and their velocities of fuel droplets were calculated for repetitive injections.The ensembled average mean velocity showed reasonable agreement with the velocity obtained by visualization. At higher load conditions, the atomization was achieved at high speed air flow such that the mean diameter was reduced. From medium to full load conditions, the fuel droplets were distributed in a tube-like profile due the shape of the nozzle. The first group of droplets had high velocity and small mean diameter in contrast to the second group. Relative slip velocity was not so small even in the fine droplets within the air flow from the injector as can expected.