The quantum transport of electrons in a T‐shaped waveguide structure is investigated using the tight‐binding model. We take into account electron‐electron interaction in the resonator region within the mean‐field approximation. The scaling rule breaks down in the interacting system and the effect of the interaction is significant when the sample dimensions become large compared to the effective Bohr radius of electrons. The nearly perfect reflection due to the transmission resonances is shifted to higher energy as the repulsive interaction is increased. The interaction effect in the presence of short‐range disorder is also examined. ©1995 American Institute of Physics.