International audienceThe purpose of this paper is to construct a compact symplectic (non-nilpotent) solvmanifold M6=Γ/G of dimension 6 which does not admit Kähler structures. We show that the minimal model of M6 is not formal by proving that there are non-trivial (quadruple) Massey products, however we remark that all the (triple) Massey products of M6 vanish