An electrical connector includes an insulating body and a first terminal module. The first terminal module includes a first insulating portion and a number of first terminals. The first terminals include a number of pairs of first signal terminals and a number of first ground terminals. The first insulating portion has a first side surface and a second side surface. The electrical connector includes a first metal shield mounted to the second side surface. The first metal shield is located between the second side surface and the insulating body. The first metal shield is in contact with the first ground terminals. The present disclosure increases the shielding area and improves the quality of signal transmission. The present disclosure also relates to an electrical connector assembly and an electrical connector module including the above-mentioned electrical connector.