Flow development in the bubble columns is of importance for the sparger design and reactor scale up. In the present study, axial development of local gas holdup and liquid velocity in two bubble columns (0.5 and 0.8 m in diameter, respectively) operated in the churn-turbulent regime was experimentally investigated. The results show that gas distribution type, superficial gas velocity and column diameter have remarkable influences on the flow development. Compared with the near-wall aeration, the uniform and central aeration will generate more rapid flow development. The observed strong influence of the sparger type on flow development shows an opposite trend to the reported findings. Furthermore, increasing superficial gas velocity or decreasing column diameter will reduce the entrance region length. The scale effect indicates that for the large-scale industrial bubble column reactors, a large portion of flow region may be covered by the distributor region rather than the well-developed region.