The invention relates to a sealing device (3) for a motor vehicle heat ex-changer (4) consisting of a plate (5) comprising a central cavity (12) configured to allow the passage of a tube of the heat exchanger, characterised in that at least two opposite end edges of said plate (5) are each provided with snap-fastening means (8), each capable of engaging with complementary snap-fastening elements integrated into a recess located in a support frame of the heat exchanger, and characterised in that the sealing device (3) comprises an elastically deformable sealing means (14) arranged around the central cavity (12) formed in the plate (5).