Swirl effervescent atomizer consists of a combined atomization mechanism of swirl and effervescent atomization which benefited each atomization. Unfortunately, external and internal flow structures of this type of atomizer and their relation to operating conditions and atomizer geometries were not well understood. In this present study, influence of operating conditions and atomizer geometries on the spray breakup characteristics of swirl effervescent atomizer was investigated. The atomizer was designed, fabricated and later tested with water as the working fluid and nitrogen as the atomizing gas. The interaction effect between swirl-generating vane angle and gas to liquid ratio (GLR) on the characteristics of the spray breakup were investigated. Box-Behnken design of experiment was used in investigating and analyzing the interaction effect. High-speed shadowgraph technique was utilized to record the videos of the spray structures. The video recordings were converted to image sequences and analyzed using image processing software. It was found that an increment of either swirlgenerating vane angle or GLR has resulted in a shorter spray breakup length. The spray breakup length shortened from 18.65 mm to 9.77 mm with the increase of the swirl-generating vane angle from 30° to 60°. Increase of GLR from 0.000388 to 0.000998 has reduced the length of the spray breakup from 18.65 mm to 12.14 mm. The interaction of swirl-generating vane angle and GLR has caused the spray breakup length to reach 6 mm at the highest settings of both parameters. This length was not achieved by the individual effect of either swirlgenerating vane angle or GLR.