An electrical connector includes a housing member and a number of contacts attached to the housing member. The contacts include a number of first contacts and second contacts arranged side by side along a transverse direction, respectively. The second contacts include a first pair of differential contacts, a second pair of differential contacts and a grounding contact disposed therebetween. At the mounting end of the electrical connector, a space between the grounding contact and the differential contact of each pair most adjacent to the grounding contact is much bigger than any internal space between the differential contacts of each the first or the second pair. As a result, a rear wall of the housing member can provide adequate area for easily mounting a fiber optical lens.