An electrical connector assembly includes a receptacle connector and a plug connector mateable with each other. Each of the receptacle connector and the plug connector defines a first mating face and a second mating face perpendicular to each other in response to mating along the front-to-back direction and the vertical direction. Each of the receptacle connector and the plug connector includes a plurality of contacts composed of a plurality of first contacts and a plurality of contact units alternately arranged with each other along the transverse direction perpendicular to both the front-to-back direction and the vertical direction. Each contact unit includes a second contact and a third contact wherein the second contact is closer to the second mating face than the third contact is while the third contact is closer to the first mating face than the second contact is.