An electrical connector includes an insulating housing having a number of passageways and a number of dividing walls extending from a rear side of the passageways; and a number of contact modules received in the insulating housing and arranged along a first direction. Each contact module includes an insulator and a number of conductive contacts received in the insulator. Each insulator includes a first section and a second section. The dimension of the first section along the first direction is larger than the dimension of the second section. When the contact modules are assembled to the insulating housing, the second sections are received in corresponding dividing walls, respectively.