Molecular and crystal structures of a series of model compounds of poly(m-phenylene isophthalamide) have been analyzed by the X-ray diffraction method and the various types of 3-D hydrogen bond network structures have been clarified. The twisting angles between benzene and amide groups are in the range of 25-40degrees, which is common to all of the analyzed model compounds and the parent polymer itself and could be reproduced well by the energy calculation with the nonbonded interatomic interactions between the benzene and amide groups taken into consideration. The molecular conformation, the packing mode of molecules, and the intermolecular hydrogen bond network structure were found to have good correlation with each other and could be classified systematically into several groups. This classification should be important for the energetic interpretation of the formation mechanism of the 3-D hydrogen bond network structure.