The most stable molecular packing systems of aromatic polyester molecules have been investigated by molecular dynamics (MD) simulations performed for decamer (ten repeating units) of p-hydroxybenzoic acid (HBA) in the nematic phase. The MD simulations were started from eight possible packing structures. Among them, we found the polar ordering structure with the intermolecular ester carbonyl groups aligned in the same direction is energetically most favorable. This is consistent with our previous experimental observation for the second-harmonic generation (SHG) intensity measurement.