Abstract: A joint assembly for plastic tubes including an annular caulking element having a substantially triangular cross section, opposite annular ends thereof being adapted to be caulked into the outer peripheral surface of a plastic tube to be connected by the wedging action applied by a fastening structure, said caulking element being composed of two annular members arranged to be axially compressible toward each other while defining an annular groove therebetween, and an annular elastic sealing member being disposed in said groove and being adapted to be bulged out, radially inwardly to be pressed against the outer surface of said plastic tube under said axial compression of said two annular members.