Julien Grivaux Tian's invariant of the Grassmann manifold (267K, Postscript) ABSTRACT. We prove that Tian's invariant on the complex Grassmann manifold G(p,q) is equal to 1/(p+q). The method introduced here uses a Lie group of holomorphic isometries which operates transitively on the considered manifolds and a natural imbedding of the product of p copies of the one-dimensional complex projective space in G(p,q).