Using density functional theory and non-equilibrium Green's function formalism, we investigate the effects of asymmetric nonequi-length carbon chains on the electron transport properties of diphenyl-dimethyl molecule. The results show significant odd-even dependence: the rectification appears only in the hybrid nanostructure with odd carbon chain on one side and even carbon chain on the other side, while it is negligible in those with odd/even carbon chain on both sides. The mechanism for the odd-even dependence of rectification is analyzed by the bias-dependent transmission spectra, evolution of molecular orbital levels, their spatial distributions, and projected density of states with the applied bias. (C) 2014 Elsevier B.V. All rights reserved.