A mechanical seal assembly to be used in sterile applications comprises a pair of co-operating seal rings (2, 5), one of which is held rotationally fixed and the other of which is provided to rotate together with a rotating component, wherein one of the seal rings is axially movable and biased by a spring against the other seal ring, a retainer housing (1) at which the rotating seal ring is retained near an axial end thereof, a mounting member (12) which may be mounted rotationally fixed at the rotating member, and a rotatory force transmission device (10) for transmitting a rotatory force between the mounting member and the retainer housing. The rotatory force transmission device (10) comprises a transmitting ring (15) retained in press-fit at the retainer housing (1) near the other axial end thereof, the transmitting ring including at least one protruding engagement member (20) engaging in an aligned recess in the mounting member. The retainer housing may therefore feature a desired smooth outer periphery without any dead spots.