The detailed description of the crystalline structure of a channel type epsilon clathrate cocrystal of syndiotactic polystyrene (s-PS) is presented here for the first time. The proposed structure is based on X-ray diffraction experiments, molecular mechanics calculations and infrared measurements. The guest molecule is p-nitroaniline (NA), a highly polar molecule which makes its cocrystals possibly suitable for nonlinear optical and piezo-electric materials. X-ray data are interpretable in terms of the orthorhombic unit cell (a = 1.62 nm, b = 2.20 nm and c = 0.79 nm) and the space group Phen already proposed for the nanoporous epsilon form indicating that the crystal packing of the chains in the clathrate form remains substantially unaltered in respect to that of the nanoporous form. NA guest molecules are placed in the channels delimited by the chains with a high degree of freedom along the channel axis but with their dipole almost parallel to the chain axis and forming with their main molecular plane an angle of nearly +/-20 degrees with the bc plane. Moreover, in each channel guests are stacked all with a same relative dipole orientation and are not uniformly distributed but arranged in "couples", in which molecules are linked by hydrogen bonds. A quantitative analysis of the crystal structure of the nanoporous s-PS epsilon form is also presented.