Abstract. We study the curvature of the moduli space M g of curves of genus g with the Siegel metric induced by the period map j : M g → A g . We give an explicit formula for the holomorphic sectional curvature of M g along a Schiffer variation ξ P , for P a point on the curve X, in terms of the holomorphic sectional curvature of A g and the second Gaussian map. Finally we extend the Kähler form of the Siegel metric as a closed current on M g and we determine its cohomology class as a multiple of λ.