Non-circular nozzle geometries are widely used in many industrial processes with submerged gas injection for altering the centerline gas holdup to intensify the reaction process. However, the effect of the nozzle geometry on the centerline gas holdup is rarely investigated. In this work, hollow circular-shaped, gear-shaped, four-flower-shaped and multi-hole-shaped nozzle geometries are utilized to investigate the centerline gas holdup by wire-mesh sensors and digital image processing. The results reveal that the centerline gas holdup is influenced by nozzle geometry, axial distance and gas flow rate. The centerline gas holdup for hollow circular-shaped, four-flower-shaped and multi-hole-shaped nozzles is larger than that of the gear-shaped nozzle. The correlations for the centerline gas holdup are obtained based on modified Froude number Fr_m and dimensionless axial distance z·do-1via regression analysis. The correlations for hollow circular-shaped nozzle geometry obtained in this study are validated with experimental data from this study and the literature.