Abstract. We consider the Heisenberg group H n = C n ×R. Let ν be the Borel measure on H n defined by ν(E) = C n χ E (w, ϕ(w)) η(w)dw, where ϕ(w) = n j=1 a j |w j | 2 , w = (w 1 , ..., wn) ∈ C n , a j ∈ R, and η(w) = η 0 |w| 2 with η 0 ∈ C ∞ c (R). In this paper we characterize the set of pairs (p, q) such that the convolution operator with ν isWe also obtain L p -improving properties of measures supported on the graph of the function ϕ(w) = |w| 2m .