Magnetic properties of ultrathin Co film on nanorippled Si substrate have been studied. Low energy ion beam erosion of Si (1 0 0) substrate has been used to produce nanoripples with the wavelength and amplitude of modulations being 32 nm and 1.2 nm, respectively. In-situ magneto-optical Kerr effect measurements have been used to study the evolution of the hysteresis loop with film thickness. The results are compared with those of Co film deposited on polished Si substrate. Co films on nanorippled surface exhibit a strong uniaxial magnetic anisotropy with its easy axis along a direction normal to the ripple wave vector. The magnetic anisotropy exhibits a monotonous decrease with increasing film thickness. Co film on nanorippled Si surface exhibits a magnetic dead layer of 0.8 nm because of possible intermixing of Co with Si to form non-magnetic silicide. (C) 2011 Elsevier B. V. All rights reserved.