The fouling behavior of Neosepta AMX and ASM was investigated in batch and flow electrodialysis systems, using humic acid（HA）and sodium dodecylbenzene-sulfonate（DBS）as foulants by measuring the voltage drop between probe electrodes. DBS fouled AEMs; however, in the case of HA, the voltage drop of the batch system increased while that of the flow system did not change. This is because the increase in the voltage drop in the batch system was caused not by fouling of HA, but by the increase in the solution resistance. From these results, the fouling test using the flow system indicated clearly that HA does not significantly foul AMX and ASM.