A gasket for a valve of an internal combustion engine; said valve comprising a guide element defining a through seat, and a mobile stem sliding in said seat; said gasket having a central axis and comprising: - an elastically deformable sealing element, having an annular shape with respect to said axis and adapted to be arranged externally on said valve to cooperate both with said guide element and with said stem; and - a support element having an annular shape with respect to said axis, coaxially arranged on at least part of said sealing element so that this latter is radially pressed between said support element and said valve; wherein said support element comprises: - a first annular component, internally cooperating with at least one portion of said sealing element; - a second annular component, distinct from said first component, mounted coaxially and in a radially outermost position on said first component and configured to arrange in use said gasket on said engine; and - snap coupling means between said first and second components (30, 31); wherein said second component comprises a substantially cylindrical or frustoconical main body surrounding said first component, and an annular flange radially projecting outwards from one end of said main body and adapted to be mounted in a fixed position with respect to said valve; characterized in that said main body of said second component has, in a position axially spaced from said flange, an annular edge radially projecting towards said axis and defining an axial abutment for an interaction portion of said first component; and in that said snap coupling means comprise two or more hooking projections angularly equidistant about said axis, cantileverly extending from said annular edge towards said flange within respective windows of said main body and cooperating in contact with said first component to abuttingly keep it against said annular edge. - an elastically deformable sealing element, having an annular shape with respect to said axis and adapted to be arranged externally on said valve to cooperate both with said guide element and with said stem; and - a support element having an annular shape with respect to said axis, coaxially arranged on at least part of said sealing element so that this latter is radially pressed between said support element and said valve; - a first annular component, internally cooperating with at least one portion of said sealing element; - a second annular component, distinct from said first component, mounted coaxially and in a radially outermost position on said first component and configured to arrange in use said gasket on said engine; and - snap coupling means between said first and second components (30, 31); wherein said second component comprises a substantially cylindrical or frustoconical main body surrounding said first component, and an annular flange radially projecting outwards from one end of said main body and adapted to be mounted in a fixed position with respect to said valve; characterized in that said main body of said second component has, in a position axially spaced from said flange, an annular edge radially projecting towards said axis and defining an axial abutment for an interaction portion of said first component; and in that said snap coupling means comprise two or more hooking projections angularly equidistant about said axis, cantileverly extending from said annular edge towards said flange within respective windows of said main body and cooperating in contact with said first component to abuttingly keep it against said annular edge.