Dynamical motions in 4-n-octyloxy-4-cyanobiphenyl (8OCB) as studied by quasielastic neutron scattering technique in its smectic and nematic phases are reported. Analysis of elastic incoherent structure factor indicated the presence of motions of the side chain around the chain axis and the core group around the molecular axis in both the smectic and nematic phases. It is found that while chain group undergoes 2-fold jump rotation in smectic phase and uniaxial rotational diffusion in nematic phase, the core group follows uniaxial rotational diffusion in both the phases. Dynamical parameters correspond to the side group as well as the core group in both nematic and smectic phases are determined. (c) 2005 Elsevier B.V. All rights reserved.