In a two-stroke gasoline engine, the in-cylinder spray pattern and fuel atomization of an air-assisted fuel injection system is analyzed. The visualization of the spray inside of the cylinder is achieved by taking photographs through endoscope mounted in the cylinder head viewing the cylinder. The interaction between the fuel spray and in-cylinder flow motion is thus observed.The spray droplet size is measured by a PDPA(Phase Doppler Particle Analyzer) in an open chamber test rig. The results show that air-assisted fuel-injection system achieves much better atomization than the traditional low-pressure solid fuel injection system. The droplet size at the center of spray plume decreases with the increase of fuel injection rate. Also, the optimal air injection timing relative to the fuel injection timing on the droplet size is also investigated.