Recently, Chen defined an invariant &M of a Riemannian manifold M. Sharp inequalities for this Riemannian invariant were obtained for submanifolds in real, complex and Sasakian space forms, in terms of their mean curvature. In the present paper, we investigate certain C-totally real submanifolds of a Sasakian space form M 2m+ \c) satisfying Chen's equality.1991 Mathematics subject classification (Amer. Math. Soc): 53C15, 53C40, 53C25.