Let F(q)(m.n) he the vector space of m . n-tuples over a finite field Fit and P = {1, 2,..., m - n} a poset that is the finite union of In disjoint chains of length it. We consider on F(q)(m.n) the poset-metric d(p) introduced by Rosenbloom and Tsfasman. In this paper, we give a complete description of the symmetry group of the metric space (V, d(p)). (C) 2008 Elsevier B.V. All rights reserved.3094763771