The aim of this study was to experimentally investigate the effects of prefilmer edge thickness on the time-dependent breakup length of liquid sheet in a prefilming airblast atomizer using a high-speed camera. Five different prefilmer configurations were tested to investigate the effect of widely varying prefilmer edge thickness (160, 500, 1250, 2000, and 3000 mu m). The liquid volume flow rate per unit width of a prefilmer was varied from 0.8 to 2.6 cm(3)/(s.cm),and the air velocity was varied from 33.7 m/s to 83.0 m/s. An effort was made to quantify these effects on the time-dependent breakup length and its predominant frequency using an image processing technique and fast Fourier transform analysis. The experimental results showed that as the prefilmer edge thickness increased, a larger liquid volume accumulated at the prefilmer edge. This resulted in the elongation of the liquid sheet; thus, the breakup length increased and the predominant breakup frequency decreased. At a large liquid flow rate and air velocity, however, a two-dimensional wave, called a roll wave, formed on the prefilmer wall surface and triggered the sheet breakup. In this condition, the predominant breakup frequency is dominated by the roll wave, and the breakup length is influenced by the prefilmer edge thickness.