We report on the potential use of Cr-Cn-Cr as a tunable molecular spin filter. Our study reveals that by suitably engineering the number of carbon atoms between the two Cr atoms, very strong spin filter efficiency could be achieved. An even-odd oscillation has been observed both in the spin polarized conductance as well as spin filter efficiency and it is reported that only with even number of carbon atoms the spin filter efficiency of the systems become 99.99%. Results obtained from the state-of-the-art nonequilibrium Green's function based calculations has been validated by analyzing the spin polarized transmission spectra, density of states, and molecular projected self consistent Hamiltonian states obtained at specific length of the carbon chain. The modification in singly occupied highest molecular orbital on going from odd to even number of carbon atoms explains the origin of the even-odd oscillation. © 2013 Elsevier B.V. All rights reserved.