In this work, we reported on the synthesis and characterization of (Z)-4-oxo-4-ureido-but-2-enoic acid and p-toluenesulfonic acid 3-nitrophenyl ester and their detailed crystal structure information were studied. The crystallization of (Z)-4-oxo-4-ureido-but-2-enoic acid results in reduced pi-conjugation in the molecule and weaker intra-molecular hydrogen bonding. The main driving force for the molecular self-assembly of (Z)-4-oxo-4-ureido-but-2-enoic acid was found to be the strong intermolecular hydrogen bonds. Compared with (Z)-4-oxo-4-ureido-but-2-enoic acid with six type of strong H-bonds, p-toluenesulfonic acid 3-nitrophenyl ester possesses much lower melting point (110-111 degrees C), average packing energy (-3.7 kcal mol(-1)), molecular deformation energy (-0.6 kcal mol(-1)) and highest torsional angle change (9.3 degrees). This can be ascribed to the week intermolecular interaction between center molecule and adjacent molecules. (C) 2013 Elsevier BY. All rights reserved.