A connector (1) for a fluid-dynamic circuit with an improved sealing system (2) between a main body (3) having, along a longitudinal axis (X), a substantially cylindrical upper portion (4), a cylindrical threaded portion (5) and a central portion (6) connecting between the said upper and lower portions (4 and 5), and a seat (7) having a threading (8) into which the lower portion (5) of the body (30 is to be screwed; the sealing system (2) including an annular groove (11) formed in the central portion (6) of the body (3), a flared portion (12) formed at the longitudinal end of the seat (7) facing the body (3), and a sealing ring (13) arranged in the groove (11) and compressible between the flared portion (12) and the bottom wall (14) of the groove (11); the connector being characterised in that the sealing system (2) includes a tooth (21) which prevents the sealing ring (13) from slipping from the groove (11) during a screwing-in operation in that an inner wall (15) of the tooth (21) acts as stop for the sealing ring (13).