As a second part of the comparison study, microscopic features of an air-assisted fuel injector(AAFI) and a high-pressure swirl injector (HPSI) were characterized. They consist of the internal spray structure in terms of fuel mass and drop diameter, the overall atomization performance with respect to operating parameters and the drop size distribution. Large droplets are concentrated in around the head part of a spray field of the HPSI, while in the case of the AAFI, they were distributed in the tail part. Although the AAFI showed the better atomization performance, the feasible ranges of operating parameters such as injection and ambient pressure were found to be wider in the HPSI. Drop size distribution of the AAFI sprays was more dispersed than that of the HPSI. Drop size distribution of the AAFI sprays was more dispersed than that of the HPSI. However, at the well-atomized condition, it appeared to be very uniform.