A coaxial connector assembly including a plug connector and a receptacle connector each holding a coaxial terminal including a center and an external terminal surrounding the center terminal, wherein housings of the plug connector and the receptacle connector have an engageable/disengageable lock mechanism, in an engagement state, a range of relative movement between the coaxial terminals in an axial direction is smaller than a shorter one of a center terminal effective fitting length, which is a distance from a start position to an end position of contact between the center terminals, or an external terminal effective fitting length, which is a distance from a start position to an end position of contact between the external terminals, and an impedance in the axial direction range of the minimum effective fitting length is matched to a specific impedance.