Although many papers have reported suction influence on sediment transport, only few of them considered effects of suction zone length on sediment transport rate. In this study, experiments were conducted to investigate suction effects on sediment transport rate in a horizontal conduit with a suction zone with variable lengths. The results show that at the same suction intensity in the form of suction velocity ratio, the sediment transport rate increases with suction zone length, while all the data collapse if suction intensity in the form of suction rate ratio is used. Moreover, velocities measured using particle image velocimetry are used to explain the effect of suction zone length on the transport rate. Finally, a modified densimetric Froude number involving the effect of suction rate in terms of changes to the near-bed streamwise velocity is developed on the basis of this finding.